My suggestion would be to get a couple of Brodak trainers and build the first with your kids' help. Then let them build the second one with your help. Bite the bullet and get a good .049 like the Brodak. That way, they get to train with an engine that is similar(regular venturi/side exhaust/detached tank, etc.) to the larger ones (.15/.25/.35/.40) that they will move up to as they progress. This is what I plan to do with my grandson in 4 or 5 years, if I'm still around. FWIW Glen