Best solution IMO: Don't let them use social media. If they really need to communicate, just buy them a SIM and or let them use your phone and SIM to contact them directly.

And if you must let them use social media, set up parental controls on your router. I suggest NextDNS for this. And basically, monitor everything your child watches or interacts and engages with. If they're using YouTube, check their accounts to see what content they're consuming.