I don't know how single parents do it but as a father with 2 kids and having a wife it's hard enough. You get home and it's all about the kids till they go to sleep, then I have to balance going out into my garage to train and spending some time with the wife. It gets hard and after a hard day at work and dealing with kids all night it takes a lot of effort to get out in the gym. Add in there I have to take time to make food for the week to take to work so I am not eating shit while at work, then I have a 2500sqm block of land and the weekends are spent gardening. It becomes very tiring.
I think that if the single parent works the only way they can manage it to train at home when the kids are asleep. I can't see any other way.