I think all will cap the charges on kid’s phones if you request it.
Talkmobile have been so good, any minor tweeks I need, they set up immediately. Needed a new sim, came the next day and activated in minutes.
I spoke to a few other providers via livechat, they best they would offer would be text alerts when you’re about the run out but onto to number being used, which would be ignored, with EE you have to reply with a text to say you’d like some more, very expensive data please, which would happen, almost imeadiatley and then again every 30 mins forever more.
I didn’t try them all though and I was a bit hampered by the fact I don’t habe a personal mobile contract I could add a sim too.