Been there, done that, many times. Including groups that meet in libraries.
A couple have been marvy. Several have been meh. One was extremely destructive.
That said, a good group is worth more than gold and should be cherished and protected. My experience is that any group that is open to anyone wandering in isn't going to be one of those good groups--however they are places to meet people to form such a group.
The thing about any writing group is to know distinctly what it is you want from it, first and foremost, and to pick a group that's geared toward it. Critique? Support? Cheerleading? Socialization? General help? "All of the above" is nice, but groups aren't that generalized, especially if they're small. There will be one, perhaps two things that they will do extremely well and that's it. And it's rare to find a group that's conscious of what it does really well so you can't just ask them.
Actually, if you ask them, they'll probably tell you that they're a critique/support group. IME, the vast majority of them start that way, at least, and probably use critique as the basis of their meetings. That leads into other questions--does your (theirs and yours) definition of critique mesh? Do they actually do that work? Are they knowledgeable of what you write? (For instance, I wouldn't have a clue how to comment on the OP's work since she writes for children, so anything I had to say would be useless because of my ignorance on her genre/age group.)
If it's socialization/support/cheerleading, that's a little easier but the catch there is that many groups don't think that's really "enough" to base a group on so they try to do critiques and that's a setting that I've found damaging. If people are doing the work, then people expect you to take their comments, and that mixed-message often tears the group apart or makes the socialization aspect unpleasant.
Unless you're clear on what you want from the group, you won't really be able to judge whether or not this group is good for you. Once you figure that out, go and see what they have to offer. That's the only way to see if you'll actually mesh or not. And if you don't, say polite farewells and keep in touch with individuals, if you want.
I met my best friend of 25 years at such a group, FWIW. The group sucked Gilbraltar through a bar straw, but she is a treasure I still value today. My other valued beta reader was met through another such group about 10 years ago.
Good luck with it, Jilly.
