Still you should check if somehow your son didn't use the sync option or you are sharing somehow the same account. On routers all your computers get an internal IP inside the router but the outside IP is the same for all of them. Maybe google detects that the other machine didn't have the updated cookie (with your search queries) and downloaded when the other computer connected to the network.

Also is your son using his own Google account (for Google Play for example) or is he using your account (maybe to BUY apps or stuff like that)?

Please try to reproduce the problems and check each and every sync option. Better it would be to post some screenshots with the problem!

P.S. I never quoted your post, when I was discussing about DDG and stuff like that I was discussing with the rest of the users here.

If you want your son not to be exposed to stuff not intended for his eyes here is the best solution:

• Open up your router configuration and check which internal IP was given to him.
• Go to DHCP setting and add a custom rule for his ip to switch from dynamic to static (so he would always have this inside the network).
• Add custom rules with bad websites that you know he could visit, or you visited and you don't want him to visit.
• Set those custom rules only for that static IP and your kid is safe.