You can rent one of those "surrey bikes" at the BW that you drive like a car that I know a five year old and an eight year old would get a kick out of. You ride along the boardwalk and can go around the lagoon for about a 20 minute to hald hour trip. There are two inclines on the route that are hard to pedal up even with several adults on a big bike that always make us laugh as we attemt to get over them. We rent them once every time we are there and we realy enjoy it. My kids are quite older than yours now but I'll bet we'll all get on the bike when we are there in late July.
There are also some carnival-style games on the BW (not free) but I don't think they really open up until early evening. Maybe someone else knows the timing.
As far as the wandering entertainers go (jugglers, guy on stilts, etc.) I have seen them but I have never seen any posting of times or hours they are on the BW. I think that that is part of the atmosphere there- random entertainment on the BW.