Hi
We go to Arenal d'en Castell and the hotel is called Aguamarina. If you book independently it is possible to go AI not sure with tour operators as I don't use them. I know most of them do the hotel. We go half board though but I have seen that they do AI now.
The hotel is very family oriented, maybe not for older teenagers though. We went last year with two other families and had a great time. As a family this will be our fourth year going back and our oldest is 10. Youngest was 18 months fist time we went.
Resort quiet but the children have lots of activities and find friends easily. The hotel have some sort of entertainment every night so we usually just stay there as the children want to play in the playground, with their friends, do the mini disco and the rest. There is two play areas for children nearby and a few bars etc. The hotel sits on the beach so we walk up and down to the beach just like we were walking to the pool area.