Only time I ever had fun playing Bonk 3 was with my 7 year old playing two player. I think 1 and 2 are demonstrably better.
Well, I've really enjoyed playing Goof Troop, Joe & Mac, Pocky & Rocky, etc... for SNES with my 6-year-old and my 7-year-old sons, so we'd probably enjoy playing Bonk 3 as well... Now to find a reasonably priced copy...