Surf mats with handles are great and still fairly cheap at $30-$50 new
$35 at KMart will buy you a skim board with handles that is a good multi-purpose toy for <8yr olds
>$220ish will get you a superb quality foam board from
www.katanasurf.com/ I reckon at 4 yrs old most kids will be best with you as co-pilot. There are some that have "it" and can go it alone but that's maybe 5%. For the rest, get a BIG board that you can both lie on and catch small waves. The main aim is to get them to understand it is FUN and SAFE, sometimes if the go by themselves and stack it they will never want to do it again.
Good luck!!

