Are they still young enough to appreciate dinosaurs? If so a walk on the south west beach below Compton will result in you finding fossilised footprints. There is also a dinosaur museum along the coast eastwards.
The IOW Pearl centre is along the south coast before Compton. Princess Diana’s pearl dress is on display and there is a huge range of pearls and jewellery for sale. It’s as informative as it is a shop.
The Needles has a small pleasure park, not brilliant but there is glass blowing and a chair lift down to the beach. From there you might be able to have a rib ride out to The Needles if they still do it.
There is a great botanical centre at Ventnor which might be better this year given the damper atmosphere.
One August I recall sitting on a hill up by the radio towers above Ventnor and watching a firework display in the bay below.
Great walks along the Landslip and in the woods in the south west.
Pubs: The Spyglass Inn at Ventnor, The Sun Inn at Hulverstone and the Bugle just above St Catherine’s Point (another great walk round the lighthouse).
Pony trekking near Yarmouth.
Osborne House (something I have yet to visit).
Hope that helps.