Hi Ellen
I think all 3 resorts would be great for kids, Playa has now got its own children's pool area and lots of activities for children eg a games room, small football/basketball court etc, also its right on the beach which is great.
We've only been to Son Antem once, the townhouses are wonderful, I think one of the best in Marriott, they have a proper living room, two upstairs bedrooms and bathrooms, lovely big staircase, patio doors leading onto your own small garden and then just a little stroll down to your pool, which was always empty when we were there. There is also a hotel on site with its own pool, spa, golf course and restaurants. The only downside of Son Antem is that it really is in the middle of nowhere and you would need a car, even to just get a few groceries, also there is no beach on site.
I think you would love any of the resorts but perhaps you would be better in Playa or Marbella, there's more places to visit more generally in the vicinity. Also I think you'll get a trade especially if you try for early Summer, ie before about 20th July, as that's when most schools in UK break for Summer holidays, not sure if this is same for rest of Europe.
If you want any further info, just ask, also have got photos of Playa if you wish me to send you some
Lynne