My son started using Look pedals (not Keo - the old, Delta standard) when he was 9. He fell down when stopping twice, after that, he had no problems. He's 11 now, and is still using his Looks.

We tried SPD pedals, and he couldn't get into them easily... they required too much downward pressure, even with the tension turned down. He is not very heavy - 70 lbs. My son also thought that the SPD pedals were "uncool" because the other roadies in our club weren't using them, so we abandoned the SPDs pretty quickly.

I just bought him some SIDI Genius shoes. He's real proud to have the same gear that most of the riders use in our club.

I really think the clipless pedals improve his technique too. He spins faster with them, and his form looks better when climbing out of the saddle.