First of all, I would get a butterfly net, and scoop the bees out of the water. Dump them on the ground somewhere that the kids won’t step on them, and any live ones will then fly off when they have dried out a bit.
Second I would find out whether the beekeeping neighbor supplies water for their bees. If not, they should. To make it more attractive to bees, they can even add one teaspoon of chlorine bleach per gallon to make it smell like the swimming pool. 
Many cities have regulations for urban beekeepers, requiring water provision for bees - you might want to check that. If they are not in compliance, you have a right to file a complaint. If their hives are not registered with the city, they may be subject to some big fines. OK, not very good for neighbor relations, but you may have some rights to action if the neighbor is not being helpful.