YY agree it helps to understand the cycle of how they reinfect.
The live worms come out at night to lay eggs while the person is asleep. The eggs are laid in a sort of mucus which is irritating, so you/DC scratch, either in sleep or throughout the day.
Eggs get transferred to the fingernails and then to the mouth while eating. Or if DC scratch and then touch toys/other DC's hands they can transfer eggs to other DC who may then ingest them.
There are all sorts of scare stories online about how long the eggs can supposedly live when they're not on a person but I think this is highly unlikely and just designed to push you towards the idea of a "parasite cleanse" (which, just don't even google it, just no. It's craziness, nobody should do this.)
Break the cycle by discouraging bum-scratching (undies or even better a nappy at night, not a pull up, one with tabs, undies straight in the wash in the morning) and if you notice anyone/yourself doing this, wash hands straight away.
And help eggs not stick to hands, with short nails. And encourage frequent hand washing, esp after the toilet, before eating and after doing shared messy play type things e.g. playdough, sandpit. Also make sure to wash hands after changing underwear which has been worn at night, helping DC with toileting, and I added a hand wash after putting dirty washing in the machine (and this now feels so natural I continued doing it because really - you are handling dirty stuff there).
Lastly, might be harder, but try to discourage fingers-in-mouth. Thumb sucking, nail biting. If these things are habits which can't be broken, then wash hands before doing them if you can.