Jade is promoted as ideal for families with children; youthful adult couples and singles. However on Deck 12 it has 3 swimming pools one for children so this should help and yes try to avoid school holiday periods will also help. As far as sunbathing goes given the time of day; direction of the sun and the wind movement caused by the ship motion you need to find your own little nooks !!
Choose a different cruise ship and line if you want to avoid children. Jade has a HUGE pool area for youngsters to have fun including a high water slide. Its a FUN ship. maybe the wrong one for you (not being rude its just geared up for families etc.).