This REGULARLY happens with a friend of mine as well.
There were 3 of us who were friends at school (but mostly when we were around 16-19), and then for various reasons we drifted apart.
But we reconnected about 4 years ago now. One of them lives about 15 mins from me, and the other lives about 30 mins away. The one who lives closest, I've seen multiple times a month, but the other is INTENSELY hard to pin down to anything.
We met up for a cream tea afternoon in late November, pinned her down to a zoom catch-up in April, and that was it. Multiple times we've invited her to "coffee in the back garden", but she's always busy or working. Then she said she didn't want to go out because her husband has asthma. From her socials, it strongly appears the family haven't left the house since this all kicked off. They have 2 primary school aged daughters, but nothing to suggest they've met up with friends, or been anywhere either.
It's always been a bit frustrating that she's SO hard to pin down to anything. But now we are actively concerned about her... But short of driving round her house and physically pulling her out... we can't do anything.
We long-ago accepted that, of the 3 of us, while she's lovely and we adore her, she's always going to be the "flaky" one who can't commit. It's not our fault, or our problem. We'll keep inviting her to things, because we love to see her, but we're not not going to "pander to the flaky". This is the date and time something is happening. If she can come, great! If not, we'll have a nice time anyway, just as a twosome.
OP: If childcare is a sticking point, could you stick to "kids welcome" meet-ups for now? A picnic in the garden? A play at a local park?