K.H.
Miralax is not a laxative so does not work after 1 dose overnight like others , it is a softner and helps to keep the BM's regular and at a normal texture , so it would need to be given everyday , or every other day at least , also finding the right dosage for your child can be tricky , my son used to need it on a regular basis but has now outgrown the need for it. If you give your child Miralax every day after 2-3 days you will see a BM , also like others have said keep dairy at a minimum and this causes constipation and try and get him to eat fruits like grapes , strawberries , clementines and plums rather than binding fruits such as banana.