Too bad. Any beekeeper would have captured them and placed them in a hive. Usually for free. A call to animal control, county agriculture agent, or city/county health department would probably have gotten the name and phone number of several keepers.
When bees gather like this, they've followed a new queen that's left an existing hive. They were not planning to hive in the swingset - that's just where the queen stopped to rest.
Bees may well be one of the most important animals on earth. Without their pollination, there would be much less food plants, flowers, etc.
Guarantee they were not africanized. I've been swarmed twice. The africans will kick your *** and not let go. Just for getting close.