In Illinois, child custody may not be modified until at least two years after the original custody order, unless the court believes that the current custody arrangement will endanger the child's physical, mental, moral, or emotional health. (thespruce.com)
However, if there has been a substantial change in circumstances after the entry of the original custody order and a change in custody would be in the best interests of the children, the courts may modify custody and visitation arrangements. (tampadivorceattorney.com)
That is a matter underlying the original custody order in 2011 and a continuing theme in subsequent parenting orders. (macleanfamilylaw.ca)