Hey, Im reons mum, he started on 30's when he was just 5yrs old, but they were to strong for him to do anything much more than walking and a little joging and a little jump, he is now 7 and still is developing, i would recomend that 3yrs is very young, do be very carefull, Reon was lucky to have many pro's around him to keep him safe, but there was always the worry of his developing bones etc,
there are lots of protection ideas i used, if you want any help pm me, but please think it thrugh before trying to strap him in, and look at the spring in the back of his leg, he may not be able to bend his knee, i hope i don't sound negative, its only advice, just think safety first, then Fun.