So many great places to stay on the Isle of Wight - if you do go be sure to get an Isle of Wight Tourist Discount Card www.iowtouristcard.com - you can save lots of money during your trip - we did last year - We are so looking forward to going back this year and hope the weather is a bit better this time!!
Bonchurch has lovely rock pools but not much sand, there's a couple of cottages there if you Google.
We've stayed in Chantries in Bembridge - beach was 5 min walk and has sand, rockpools, cafe and lifeboat station (and Co-op).
Scallop Shell Cottage and Manor Farm cottage are owned by same person and although £££ and not near a beach, have everything you need baby-equipment wise. I was impressed.
Compton bay is fantastic - sand, surf, pools - but toilets/car park and beach are separated by steep steps.
We've spent a lot of time on what's probably not quite Sandown beach- the non-Shanklin end by the yacht club. Toilets, foot showers, a slope to walk from the car park to a lovely sandy beach. Easier with loads of stuff!