In families where grandparents spend time with their grandchildren, 43 percent of the children’s parents report clashes with the grandparents over parenting choices and household rules. Topping the list of conflicts are disagreements over discipline (noted by 57 percent of parents), meals and snacks (44 percent) and television and screen time (36 percent), according to the University of Michigan’s National Poll on Children’s Health. It involved a nationally representative sample of 2,016 parents with at least one child age 18 or younger. On discipline, 40 percent of parents say grandparents are too lenient, but 14 percent say they are too strict. Other areas of disagreement cited by parents include manners, safety and health issues, bedtime, instances of treating some grandchildren differently than others, and posting on social media of photos and information about the children. Parents say that disagreements sometimes stem from changes in parenting practices since grandparents had young children — such as not spanking, putting infants to sleep on their back now instead of their stomachs or using booster seats longer than in the past. Results are mixed when grandparents have been asked to change their behavior, with parents saying that 47 percent did change, 36 percent agreed to change but did not do it and 17 percent refused. About 15 percent of parents say they have limited the time grandparents spend with the grandchildren because they have contradicted or interfered with the parent’s choices.