Hi
I would have to recommend Los Alcazares , near the airport . Its on the Mar Menor , so the water is warmer , and perfect for children 4 to 5.
Our 5 year old was with us , last year , and it remains shallow for 100 yards or so , no waves , plenty of parking , and some nice beach huts for lunch.
Perfect !! Head for Hotel Narejos.
Leighton