Do children sleep among adults?

It is reasonable to say that children should not sleep together, otherwise the breath and harmful substances exhaled by adults will run into the children's bodies, but I found that if the children come out of their stomachs and sleep in the crib all the time, the children will adapt well, and let them sleep in the crib in a few days, and he will keep crying. He has realized that there is no one around, so you can't stand it, or you and the baby will sleep in the same bed.