I agree... below a certain age, there isn't even a worry about their peers' reaction. For example, if the wee one is four, peers won't even understand it's a big deal unless somehow their parents get involved. And FTM transition is so complete and, frankly, awesome (in my opinion, at least compared to MTF) that in a year or two no one will suspect a thing, ever (assuming FTM is the direction you are going; editing my post because I realized I based that assumption totally on your mention of the use of binders... please accept my apologies if that is not the case).
If they're older, more care should be taken... it's easy to get ostracized at school, etc. I'm going through this right now with my 11-year-old (separate thread).
*hug*