my child sleeps with mouth open, what to do   

Consult a paediatric to check whether the child’s airways are open or not so that the child can breathe normally and naturally. If the baby is say of 0 to 6 months old, sometimes their nostrils get blocked and they have to breathe through their mouth. So they keep their mouth open while sleeping. In this case, you should keep a check about child’s cold infection so that mucus/bogey does not develop in the nostrils. This can occur to older babies of 2 to 3 years also because of the same reason of blocked airways. So if the doctor feels the need for further check up, he can get an x-ray done or even other reports required to further understand the condition.