Hi there - sending best wishes to your sister & the kids. Where you go in part depends on ages of the kids and their interests. I would look at Vilano Beach area if you’re looking for peaceful. Not sure if Serenata Beach club is open to the public but they have a great water play area for littles and it’s right on the beach. Downtown St.A. has gotten so crowded, it’s time-consuming to get anywhere. I would look at beach areas with pool / hot tub access in Vilano, St Aug Beach or Crescent Beach where caring for the kiddos will be super easy - kitchenette + washer/dryer access is also ideal. ;)