The best restaurant on the club is La Finca.
The same people own the Si! Bar and restaurant which is more pizza/pasta and geared up for families.
There is a restaurant called La Canela, half way down the tree lined road leading to the club entrance that is worth a visit and also La Rusticana, on the same road but past the club entrance and on the left. (the Portman Road)
Also pizza pasta that is ok with kids is Luigis up at Las Lomas, although we tended to avoid the club owned restaurants.
The main club house is ok for a coffee/snack/ tapas and has a view over the golf course so you could watch your son playing up the 18th
Cartagena is worth an afternoon for architecture,bshopping, tapas bars. Drive on to the far end of the marina, not the port, and park up. There are lots of little streets leading in from there with shops/ bars/cafes.
La Cala is the beach restaurant mentioned up thread. It is open seasonally so may be closed now.
There are some nice fish restaurants on the harbour at Cabo de Palos (15 minute drive).
Don't know if the main resort pool is still open this time of year. Are you in the hotel or a villa? The pool up at Las Lomas is open year round I think.