I go out of my way to see my closest friend regularly.
The others I kind of alternate.
Sometimes I take a random half-day off work and meet someone for lunch.
If I've a significant amount of time off work, I try to catch up with people. I'd a week off work at Easter, and I messaged a few people in advance, saying, "So, do you wanna meet up". I might meet two or three people over that week. My DC is an adult now, but I did this even when she was small. Sometimes I had to bring DD and warn the friend, "Right, we've probably a good hour before she'll get bored with her toys/colouring book etc. Tell me all your news". This is probably when she was seven or eight years old though, not when she was three.
If I haven't seen someone for a while, I'll ring them or send them a WhatsApp, asking how they are and telling them my news. Or send a Facebook meme - "saw this and thought of you", type thing. It's nowhere near as good as a meet up in person, but it's a way of keeping in contact and keeping the friendship going.
I had a casual friend at work and she left a few years back. She has three kids (I have one) and hers are younger than mine. We don't live anywhere near each other. Anytime something happened at work, I'd message her to tell her, and we'd exchange news and photos of the kids etc. We finally met up earlier this year. We calculated that it had been 7 years since she left work! Those occasional WhatsApp messages and photos had kept our friendship alive all that time. When we parted, we agreed that it would probably be ages before we meet up again. In the meantime, we'll keep up with the WhatsApp messages and photos.
I know it's really difficult when you're juggling so many balls. But it's important to keep those friendships going. At some point, your DC will grow up and fly the nest. Sadly, your parents may pass away. In my case, my husband left me. You might look around one day and wonder where your friends went and why you're so lonely. Anyway, sounds like I'm preaching to the converted and you're looking at ways to avoid that.