When you give your toddler MiraLAX it should begin working within 24 to 48 hours.
However it can take up to 1 to 2 weeks of taking the MiraLAX for your toddlers stools to finally become consistent and normal again.
After giving the toddler the MiraLax they should begin pooping at least somewhat normally within 2 to 3 days.
If your toddler hasn't had a large stool mass at least once during the 3 day clean out of their bowels with MiraLax then you should take the toddler to the pediatrician as they may have a more obstructed bowel or the constipation may require further medical treatment.