There's adult content so protecting kids from gambling isn't the only problem. Parent can't let their kids use the net with out restrictions because of harmful content. Gambling's a big problem ppl don't want their kids to learn about it but there isn't a way to monitor the ads they see.
I don't know how many but some probably are when they are valuing the protection of their kids from the adult contents and the other contents that are inappropriate for the kids. The penny that they pay for the subscription monthly is worth it for them and that's why it's a way to protect their kids from such contents. While we can't protect them when they're away from us and when they're going to somewhere else, it's best not to allow them with gadgets outside the house to monitor the activities that they're doing on that gadget.