For those of you with little ones who you hope to get into tying flies, I can share a few things that I've learned. I started tying flies at the same time that my oldest son, now about to turn 10, was born. I researched everything online before deciding to buy a DanVise, which was/is a fantastic vise in every way except for the relatively soft jaws, which eventually wore out twice for me. The first time was my fault, but it was soon enough after purchase that I could return it for a new one. The second one was NOT my fault. The metal in the tips is just not firm enough to stand up over time. I still can use it for big flies, especially bass bugs, but it's not firm enough to hold dry fly hooks smaller than roughly a size 14. It is now the one of the vises that I have my kids use, and it's the only true rotary vise that I let them touch.
Having started with a rotary, it was maddening to go the other way. The very first fly I learned to tie was a Woolly Bugger, and on the very first fly I used the rotary function to spin on the chenille, the hackle, and the wire to hold it all together. I'd seen loads of videos where tiers did it the "normal" way on a stationary vise, so I understood how to do it, but, man, once I was used to the rotary, it felt like I was handicapped to go back to the stationary. I'm making sure that my kids learn how to tie on a stationary vise first because they're really not coordinated enough to make use of the rotary function until they're around 8-10 anyway.
As my wife and I had more kids, and I kept tying flies, over the past few years I've picked up a couple used lower, mid-range vises on Ebay and some cheap knockoff vises, too. My kids are old enough now--almost 10, almost 8, and 4 1/2--that I have them all tying flies, which they really like to do. Sometimes I set them each up with a vise at the kitchen table and put some materials in the middle of the table for everyone to grab and use. I made them each start out by tying very simplified Woolly Buggers in sizes 2 to 6. I let them pick the colors of the materials and the size of the hook, and then I would match the hooks and thread to what they had picked. It's fair to say that my daughter has an arsenal of pink, purple, and pink & purple Woolly Buggers. I would let them mess around the hackle, but it wasn't until this past year that my oldest two could handle tying a standard Woolly Bugger, start to finish. They still struggle with hackle in almost any other style, wet or dry.
What I can say with certainty for kids learning to tie, is that the best vice for kids under 10 is a stationary vise with a grip function like the Regal. With every other type of vise, I have to adjust the hook for them each time so that it holds, and that almost always means that I have to remove it, too, because they can't open the cam when they're finished. I have a couple of cheap knockoff Regal imitations (again, more Ebay bargains), and those work as well as the real thing for my kids. Those vises wear out after awhile, but it has pretty much matched up with when my kids were finally able to make use of something better. If you want them to have a Regal for the rest of their lives, it would be a good investment to buy them one when they're starting out. Otherwise, I'd say buy the knockoffs. I'd also recommend the C-clamp because I could crank it down tight enough that they could't move it whereas the table-top stand would tip over when they were cranking away on it because kids take awhile to figure out leverage and basic physics.
I want my kids to eventually fly fish with me, but that's still a long ways off. In order to get everyone fishing, I bought each an Ugly Stik spinning rod with a Zebco 33 reel. The youngest can cast simple weighted lures when nobody's nearby, but he needs help with everything else. The oldest are mostly self-sufficient with their equipment, but I still usually tie on their lures (so that they don't lose them from bad knots), and I usually remove their fish (so that they don't kill them). I let them work on removing their own fish when/if we're keeping them. Kids are really good at unintentionally killing fish, fwiw. My goal for my two oldest for this summer is to have some outings where they do everything, start to finish, once we're there. I doubt that we'll get there by the end of the summer, but it's possible.
So what do we do with all of those Woolly Buggers that they've tied if they're using spincasting gear? We fish a lot at a local pond that is loaded with small bass, bluegills, and some nice crappies. There's a walk-bridge that has good fishing from all sides, and I like to set them up on it with a really light bobber and a lightly weighted Woolly Bugger at the bottom and a smaller unweighted Woolly Bugger above it. They catch a lot of fish on that, especially at this time of year. The crappies love my daughters pink Buggers. If nothing is biting, I add a tiny bit of pinched-off nightcrawler, and that usually works. I also bought them each cheap Tenkara knockoff rods off Ebay, and they really like fishing with those around docks and walk-bridges, but it wasn't until last summer that my oldest two kids were responsible enough to do that together without me hovering nearby to keep them from impaling one another. I let them use my cheap fly rod setups on occasion, but they're still basically dapping with it the same as they would with those tenkara rods. My oldest might be able to cast a fly line from a dock on his own this summer, but it will need to be supervised.
For those of you that are first starting to have children, take heart and figure out ways to bring fishing and the outdoors to them when they're tiny, and then bring them into the outdoors when they're old enough. If I was hoping watching the kids, I would tie flies while they were sleeping or playing in a bouncer. I kept everything on a separate counter that was on the edge of the living room so that hooks and pointy things wouldn't get misplaced or dropped on the floor. I would literally count out my hooks when starting, place them on a magnet near my vise, and count them out again when finished. In ten years I have never had a kid get poked by a hook at home, but they have found a couple lying on the floor since I let them get started tying. (I have strong suspicions that those two things are connected to each other.) Because I never started tying flies until after I was married and had children, I was never able to crank out the numbers of flies that MH mentioned. I never really kept track beyond having a rough idea of how many hooks I was buying and using, so I'm pretty sure that most years when I was overseas with small children, I was cranking out a few hundred flies each year. Those numbers went down steeply when we moved back to SD because there have been a lot more distractions that take away time--including being on this site, fwiw--and I'm rarely tying flies during fishing weather now. Tying flies in the middle of winter, though, is a blessing from God. I hunt, too, so I'd still go out and do that whenever possible, but if you think that having kids pinches into your fishing and fly tying time, wait until you see what it does to your hunting time.
One final perk to getting my kids involved is that they now genuinely love watching fishing and fly tying videos online with me. They pick up way more than I sometimes realize as my kids--especially my daughter--will occasionally identify a fly in my fly box or use technical terms like "caddisfly larva." My 4 1/2-year-old son can correctly identify brown, rainbow, brook, and cutthroat trout. My 9-year-old son has been doing "research" projects on all sorts of fish species for a couple of years now, so he now knows more about pelagic species than I do. It's pretty dang cool.