Take them for a day out to Aleado
see the monisitry on the way back and have some lunch (hotel maripossa at la santa i think) go on a sunday may catch a spanish wedding
theres a great veiw point in the mountains opposite the maripossa which you can drive up with a large statue of christ at the top of the hill ,stunning veiws.
Aleado has a castle in the sleepy mountain village. you can make it out at night when the sun sets almost right behind the castle and the village lights up on the mountain tops.
just an option for us old folk.
The guns are definately worth a visit overlooking Cartagena bay not to far away either. But the drive through the mountains is not for the faint hearted. Great veiws however and the castle restoration is almost unreal (quality)