I didn't see an ATM there. There was one in Kadryia (not sure spelling) and in Belek I was in a money changing place and they used their card machine to cash lire.
Your kids will definately have a great time at Letoonia. There is a large animation team which do all sorts of things throughout the day. You could see that the children adored them
If you do want to venture outside the hotel I can recommend the following places to visit.
Aspendos - Fabulous ampitheatre (they do a trip there at night where they have a performance of a kind of Turkish Riverdance with fire)
Antalya Harbour was lovely
Duden Waterfall (you can go behind the waterfalls)
Rafting (Didn't actually do it but went to the area. It was quite a long drive but was beautiful)
A link to some picures. (My camera was faulty, so I've not posted many this year)
http://www.flickr.com/photos/madjap/sets/72157605212074153/