My suggestion? Some old ThinkPad. I was using a T420s for several years for online college classes. I have since moved onto a T480s.
Just looked on eBay. A refurb T470 is around $140USD and a new battery on Am*zon (if you are okay with Jeff Bozo, I am not) is less than $30. So you have two batteries that you can swap out for decent time away from an outlet and a semi recent laptop with 8GB RAM and an SSD for low power consumption.
I can PM you links if you want.
Important edit: some ThinkPads don’t have webcams! I don’t know if your kid needs to video chat for school, I know my sister had to. Make sure whatever you order had a webcam – they aren’t always present!