Inability to limit children's data usage

I am a new Xfinity Mobile user and I'm very unhappy about the inability to limit my teenage son's data usage to prevent him from using up almost the entire family allowance and getting us charged data overage fees. With Verizon, I easily just set a monthly limit, he was notifiied when he was close to going over, and when he hit the limit, his data ended until the next billing period. It was simple and headache free, fee free. Now, with Xfinity Mobile, I have been told that option does not exist and now I'm paying overage fees, which makes Xfinity Mobile much, much less interesting to me. I'm almost thinking about switching carriers again due to this one issue, which I find unacceptable.