I used to coach a 7 year old with SPDs (and he was tiny for his age). I think it would probably be challenging to find shoes small enough -- I guess you could cleat a pair of his regular shoes (I've done it with red pumps -- don't ask).

Of course, toe cages would work with any shoe.

Many local criteriums (and a few road races) will have kiddie races too! You'll see every kind of bike imaginable. I personally love when the little girls on Barbie bikes beat the little boys on their tiny road bikes, but I digress.

At his age, keep it fun!

Sanctioned junior racing begins at race age 12 so he's got a few years before he can compete in "real" races.