2) I have the Google controls. That said, its as you say kids can circumvent controls so the best thing you can do is have this conversation.
We've spoken a buch of times with the kids about how other kids will look at gore/porn out of interest/shock value but they should choose not to as its not healthy etc. And other things like staying private online, predators, come to us if they are getting bullied or do something wrong like share an embarrasing picture and its getting used against them etc.
Ultimately this one its about having a good/trusting parent child relationship I feel than via digital restrictions.
3) From the Google controls we have time restriction, both time of day and total hours.
The other thing I feel is important 1) is making sure you do things with kids. It's easy to get tired as a parent and let them entertain themself but playing board games and sports etc is so important. Making sure you have quality time beyond screens makes it a smaller part of their life. And 2) Encourage the right friendships. Put the effort to organise events with kids/families with good values as the group surrounding them will have a big impact.