Is it worth doing a day trip to the IoW with a 4 yr old?
Realistically we could be at the ferry (on the mainland) by about 10 and would need to be back off the ferry again by 5, absolute latest. Is that going to give us long enough to do anything fun or would it just be stressful?
If its worth going, where would you go? I have fond memories of Carisbrooke Castle, but that's going back 20 odd yrs, I was 6 yrs older and things may well have changed...
At 4 years old my DD just loved the sand, to maximise your time you could take the hover from Southsea (only 10mins) and then enjoy the beach in Ryde. Alternatively if driving I would visit the beach at ST Helens Duver it has rock pools at low tide. There is enough to do for a life time so should be plenty of things for a day.