Yep. Very familiar with that one. I've brought it up directly and brutally.
"Can you do project XYZ this Friday night?"
"No."
"What?"
"I did the last three. Is there a reason why Adam, Bob or Charlie cannot do it?"
"Well, they have kids. Bob's kid's school talent show is Friday."
"I have a date with a former model and a very nice nurse this Friday. Which is a more important event?"
"Wait, AND? Back to back dates?"
"Na. Same time. So, which would you be doing? System maintenance, or date?"
"... Okey, Adam or Charlie can do it."
Being single or without kids is a legit way of being discriminated against. So, don't tolerate it.