I have two FWBs. One, we only meet up very occasionally, and the other maybe once a month. (now lockdown has ended) .
The last time we met up, it was just a walk in the park one Sunday afternoon, a hug at the beginning and a hug and some kissing at the end.
We sometimes spend a night together and don't have any sex.
As others have said, it is 100% on your terms. Certainly, keep the children out of it completely, especially if it is only for sex and no other future relationship.
If you only want sex, that's fine as with my occasional FWB, and with my wife and her FWB, but with my regular one, we go out for meals, walks. shopping, cinema and so on. It is purely down to you, no rights and wrongs
Don't invite them into your home until you know the better, as you've already said.
We all know the situation and no feelings have ever developed and that has never been a concern.