You got some replies to this query last time you posted- you must have missed the thread.
Try Terra Mitica- water park.
Karting in various locations
Plenty of beaches (last year my brother had four children over and said going to different beaches was the best way he found of entertaining every one. Bought a few boogie boards, took bats and balls and took picnics kids 10-17 talked about it all the time because they went to lots of different beaches so boredom didnt creep in. He also didnt find this expensive)
boat tour from the harbour at Cartegena. Leaves at regular intervals through the day.
Water sports at Mazarron
new mall near Lorca has restaurants and crazy golf on upper floor.
Hotel Mariposa in Sierra Espuna for quad bikes, cycling and I believe kayaking.(plus good food daily and the evenings are apparently very good too)
Bike hire on Condado