I have a pet bullsnake, and we keep quail. When we had a neighbor's kid do some bird-sitting, she let the snake escape (this was somewhat our fault - the snake's enclosure had a weird locking mechanism that she didn't really understand and she had permission to play with the snake) and he killed and attempted to eat one of the quail we had been nursing back to health. He ended up regurgitating the quail because he just wasn't able to swallow past the shoulders - this is a 5-6 ft long snake, btw. We were pretty devastated because the quail he had killed had been a bit of a survivor...and also because we weren't sure if we had also lost the snake (we did find him a couple of weeks later). It's not exactly the same situation, but I'm sorry that you've lost chicks :c
I'd recommend elevating your brooders if you can. Snakes are surprisingly good climbers, but they're not magic and they have trouble climbing smooth surfaces. I think certain smells can be deterrents as well? A quick search found this page, which links to an old study:
https://pestpointers.com/smells-that-snakes-hate-and-how-to-use-them/#The 2 Scents That Snakes Hate