I would suggest, for what you need/want, to get a used phone (either an old one of yours or just buy one) and get a prepay plan. That's what I have for myself - no data, I use it mostly for texting but I do get minutes, and I can connect to my home wifi if I choose to - and it's very reasonable.
This is the plan I have:
https://www.rogers.com/web/content/wireless-products/paygo_promotions_monthlydiscount
Only 50 minutes for the year before 6 p.m., but they should be in the school anyway and not using it. Unlimited evenings and weekends, unlimited text.
That way too, if they blow all their minutes, you can choose to top it up or not.