We went to Sensatori Crete and really enjoyed it with our then 5 year old. The children's pool is fantastic and ds spent the whole day with us by the pools. He did go to the kids club once which he enjoyed. Personally I would avoid the summer school holidays as it was very busy and I sometimes felt the staff were a bit stretched. Any other questions, please ask.
We went to the Tenerife one (before DD came along) and from what I remember the kids club was excellent but you had to queue to get a place, as it was always full. This was about three years ago, so may have changed. Maybe check on trip advisor as you normally get feedback there on childrens' clubs?