Used to live in Cowes, so might be able to help.
Try Monkey Haven/World outside Newport.
Appley Beach in Ryde is nice. Good surf at Compton Beach if kids like that. Or try a bit of old-fashioned crabbing!
Chessell Pottery - decorate own plates/bowls etc - plus they do yummy cream teas.
Swimming pools in Newport, Ryde & Sandown. Cinema in Newport. I think there may be an indoor soft play place in Newport too - "Jolly Rogers Plaice", although name may have recently changed.
Lots of excellent off-road cycle tracks. Bike hire guy (there is only one main one) will drop bikes off to you & come to your rescue if you get a puncture/fed up!
If you need retail therapy, head to Cowes. White Stuff, Joules, Fat Face etc there. Added bonus of yummy sailors if you happen to be there on Sat evenings...
UKSA in Cowes runs sailing courses if kids are into that.
Hope that helps. It's a lovely place - like stepping back in time.