Sensatori is a new thing I have been reading about that Thomsons do. Seems to have pretty good reviews, particularly the childcare which you book out for the time you are there - either morning or afternoon sessions.
Have a look as they have hotels in crete, mexico, tenerife and sharm.
We're considering it for a break May/June time. I'd prefer Crete but worried about the shitty flight times and a 3 year old.
Try Simply Travel (part of the Thomson group) - they have at least one (possibly 2) properties that have creche/club facilities. We used them when our boys were little (18 months & 4 & then again when they were 3 & 6)and it was brilliant; english nannies & lots of activities, with a choice of full or half days. Now they're a bit bigger (8 & 5) we're braving a Simply property without the creche - wish us luck!!
Most of the Thomson family places have kids clubs that are included. Your 4 and 6 year old could go to them. There is also a creche for little ones but you do have to pay. We went to the Bonaire in Majorca and it was about 15 euros per session for under 3s.
First choice family resorts also have kids clubs, though again they under threes are not free.