You could try the Sever/Yug. It has basic but large family rooms and there are plenty of kids around.

Yvonne

We went to the Hotel Lilia in Golden Sands two years ago. We also have three children and were given a two room suite with bathroom. The rooms were lovely and the hotel food was great. Their website is http://www.goldensands.bg/lilia/Default.asp . We travelled with Balkan Holidays, however their flight was very basic. Make sure any hotel you choose is at least 3 stars.