My only input would be to make sure they get enough calories, vitamins, and minerals. Kids are miniature "body-builders" (literally) - not only adding to muscle, but also bone, organs, and everything else as they grow.

That's why I am not a big fan of people making their kids vegans. If you are educated you can do it right but too many people jump on the band wagon and have no idea how to feed complete proteins or aminos or how to get all the essential vitamins and minerals while cutting out animal products. It isn't easy but dangerous if done wrong.

No sane person would force their child to be a vegan.  Personally I don't think any children should forced into a dietary protocol other than "limit junk food".  Unless of course there are medical reasons for doing so.