We went to Mark Warner in Corsica with ds age 5 months. They do have UK car seats available if you want to use a taxi or hire car, and they can also arrange an all day nanny if you wanted to go off by yourselves. You can also ask to borrow one of their buggies for the day if you want, though most people took their own.
There is a little village within walking distance (10 mins or so), as well as some restaurants if you want to escape, though we mainly stayed at the hotel - we were never forced to sit with others in the evening unless they were people we were already talking with.
We found that the childcare was superb. The nannies are all English and the ratios are very good. The creche has a fenced garden with plenty of shade and outdoor toys, and the toddlers often go for walks, have a big room with loads of ride-on toys, tons of painting etc. I felt very guilty at the thought of putting my young one into the creche, but on reflection we all had a better time because of it - and I came home with some lovely artwork which I would never have done myself at that age.
There is a child's pool, separate from the adults, and I seem to remember that there was a play area - ds was too small!
Baby listening service was good and reliable. We would have prefered for ds to have been in a separate room, but didn't have the option, so landed up with the cot in the hallway section of our room (ie just outside main sleeping area in front of bathroom).
From memory it would be wise to take a non-slip bathmat.
Have a great time.