The FDA admits to years of reports of tremors, tics and obsessive-compulsive behavior in children given laxatives containing PEG 3350, the active ingredient in Miralax. A 2014 FDA investigation into the safety of Miralax discovered that tiny amounts of ethylene glycol (EG) and diethylene glycol (DEG), the main ingredients in antifreeze, were found in all batches of the drug they tested.
Furthermore, an FDA spokesperson admitted that "many of the reported adverse events were classic symptoms of ethylene glycol ingestion." Some children regularly using Miralax had blood acidity when tested, according to the FDA. This is another known effect of ethylene glycol poisoning.
There are many natural approaches to treating uncomplicated constipation in children, from simple steps like changing the diet and adding in a pre- and probiotic, to massage, biofeedback, and herbal medicines. All have a track record of safety with kids.