Growing up, my best friend spent one afternoon a week after school with me. Her mom worked that day, and my mom was a SAHM. It worked well because we wanted to play together pretty much every day anyway. I'm not even sure I realized at the time that they had arranged it, I just thought we were playing together like always.
Maybe you can work something out with a friend's family and you could reciprocate by watching the kids for periodic sleepovers, or holiday weekend or something?