Your 4 year old doesn't need a tablet any more than they need a lighter. Neither does your 14 year old. (If they "need" one for school, the school can provide it and monitor their use). If you give your child a computer, it's your responsibility to make sure they're using it properly, not the government's and not the device manufacturer's. The government's job is to make sure that you're not endangering your child and split you up if necessary. The device manufacturer's responsibility is to make sure it works and doesn't hurt you or anyone else in the course of ordinary use. Your responsibility is to not use it in such a way that it causes harm.
Allowing your child to go online is much like allowing them to go outside; you tell them what they're allowed to do, and if you don't trust them to listen to you then you don't allow them to do it. The act of having a child is taking on a full-time 24/7 job of ensuring they stay alive and unharmed until they're old enough to do it themselves. If you aren't up to that challenge, then you can't have that job and it should be passed on to someone else. You can't just shove your responsibility off to Google and Apple because you're too busy to be a parent any more than you could push it off on Sony (what you watched on TV growing up) or Macy's (what products you chose to buy). Being tech companies doesn't make them magically responsible for what you do.
If you insist on providing your child with a cellphone so you can contact them in seconds at any time of day, get them a feature phone. They offer numerous advantages: they cost less to buy, they don't break when you drop them, the battery lasts longer and charges faster, and the bill costs less (the phone is for you, not them. You don't need an unlimited plan).
The best part? This is cheaper and easier. You're literally doing less. Locking down a smartphone is hard? Great, so don't do that. Problem solved, you're welcome, I'll send you my invoice.
