Definitely volunteer OP, it will help you get relevant experience. I'm a TA now after running, and then selling, a completely unrelated business.
When I had my DC I volunteered at and helped run two baby groups, which got me some experience, then when my DC were at primary and I could have a day off, I'd go in to help for forest school/listen to readers. After we'd sold the business a job came up, I went for it and they remembered me. I didn't, and don't, have any formal primary or childcare qualifications. I've been on courses relating to specific things, but nothing general. I have asked, but I don't think there's the money. Most of the TAs I work with are the same, but highly experienced having done the role for decades. They can teach you a huge amount.
I now work as a 1:1 and generally enjoy it (off with the Not Covids at the moment). I've also been a class TA too up to year 2.
The holidays are great, but the pay is low. It's lovely having time with your DC and not using holiday clubs, but you will also catch every bug going, plus worms and nits unless you're careful.
Be wary that it also can be a career dead end and unstable. Unless you've got another income stream (high earning partner etc) or want to retrain to become a HLTA (also poorly paid for what's required) or teacher that's as far as it goes.
All in, I am glad I am a TA. The children are fabulous and funny, and at present I can afford the financial hit which means I can spend long holidays with my DC.