“Nana and Papa always let us.”My 8-year-old twins had been home from a weekend at my parents’ for 15 minutes and bedtime was proving to be a fight. They were exhausted after a weekend of late nights and refused to shower or go to bed. All they wanted was another hour on the iPad. When I said no, one of them looked at me and said, “They’re so much more fun than you.” He wasn’t wrong. My parents let the boys do things that I wouldn’t.Grandparents do a lot of babysitting, which means plenty of parents hand over their kids and watch their rules get bent. Nationally, 20% of grandparents with grandchildren under 18 provide care at least once a week, and 8% do so daily or almost daily, according to the University of Michigan’s National Poll on Healthy Aging.Jenny Elia Pfeiffer via Getty ImagesMitchell suggests asking one question. “Would Grandma do this with you standing there watching her?”A few rules tend to go first. “Food, screens and bedtime are the most common ones grandparents ignore,” said Rod Mitchell, a registered psychologist. “Those are the three you can break and still call it love.”Faith McKinney broke all three over one summer. Her grandson Zion, 7, stayed with her while she worked from home. “I let my grandson have the run of the house, which includes endless access to the snack closet,” she said. “It’s not uncommon for him to have chips for breakfast while watching hours of YouTube videos about Minecraft.” Bedtime kept getting later until one night her husband found Zion watching television at 3 a.m. “I realize that my lax behavior is over the top,” McKinney said, “but when my grandson is here, he is an angel.”“The impulse behind this is familiar,” said Melina Alden, a licensed marriage and family therapist. “Grandparents saying yes and then doing their own thing isn’t usually defiance,” she said. “It’s more often a mix of three things: genuine belief that ‘it never hurt you,’ a wish to be the fun one, or a subtle power move about their standing in the family.” Rules about food and screen time are the easiest to break, she said, “because they’re low-stakes and instantly gratifying. A cookie or an extra episode is an easy way for a grandparent to be the hero of the visit.”So how do parents tell the harmless from the harmful? Mitchell suggests asking one question. “Would Grandma do this with you standing there watching her? If yes, then it’s just a different way of doing things. If she would only do it when you’re not there, then it’s not spoiling; it’s a secret that your child is being forced to carry,” Mitchell said.For Marni Levine, it began with sugar. She babysits her grandson Jack, 3, who finds Hershey’s Kisses in bowls around her house and calls them “smoochy kisses.” Lollipops came next, sometimes before breakfast. The moment that changed things happened at the movies. “When I snapped a picture, he said, ‘Oh no, don’t let Mommy see the M&Ms,’” she said.After that, she started owning up to the treats. “Nothing gives it away like an unnaturally happy kid at pickup,” Levine said. Her son and daughter-in-law let some of it go, she said, because “they know these special treats aren’t harming the kids long-term.”But not every parent shrugs it off that easily. A parent’s reaction can be bigger than the rule itself, said clinical psychologist Naomi Torres-Mackie. “When a grandparent dismisses or ignores a parent’s request, it can bring up old emotional wounds, especially attachment wounds, that feel extremely painful,” she said. “It is a break in trust that presses on an old, tender pain spot.” Still, Torres-Mackie tells parents to keep perspective. Their child isn’t reliving their own childhood. “It is clear to children that when grandma or grandpa leave, their parents are in charge again.”Grandparents may feel they already know best, said therapist Mandy Morris. “A grandparent might think, ‘I raised three kids. I know what I’m doing.’ And that may be true. But they didn’t raise this kid,” she said.Secrecy is where a small rule can become a much bigger problem.Pyrosky via Getty ImagesStretching bedtime and letting a grandchild watch TV late at night is one of the top three most-broken rules, but it’s not unforgiveable.“Breaking a minor rule is one thing. Breaking the rule and then telling the child not to tell their parents changes the situation completely,” Morris said. “You’re teaching them to participate in secrecy between adults.” She calls it triangulation, an adult conflict the child gets pulled into. “A child should never be put in the position of having to protect one adult from another,” she said.Some rules aren’t up for debate at all, said Alden. “Naps, screens, sweets, these are preference-based and there’s room to disagree. Car seats, allergies, medication, water safety — these aren’t,” she said. “Breaking those isn’t a ‘spoiled afternoon,’ it’s a trust rupture.”Sugar and screens are the obvious battlegrounds. Kristen Coffield’s was Instagram. “My personal transgression was sharing faces on my Instagram with 350k followers,” said Coffield, who founded the platform Active Grandparenting. Her daughter combed through the entire feed and had every full-face photo taken down.“I was embarrassed, and I had also built an entire brand around being a good grandparent,” Coffield said. She deleted them and never posted another full-face photo. “The only way forward is through the discomfort,” she said, “the hard conversations, the owning your mistakes and the willingness to work with parents.”What happens after a rule is broken can matter as much as the rule itself. One of Mitchell’s clients learned about a secret when her young daughter let slip, “Grandma and me have a special rule about cookies.” The client raised it with her mother, who said, “So I’m the villain now?” There was no apology. Instead, the client ended up comforting her own mother. When the grandparent becomes the injured party, Mitchell said, it can do more lasting damage than the broken rule.Some therapists don’t think any rule is too small to matter. “A breach is a breach,” said David Simonsen, a licensed marriage and family therapist of 26 years. A grandparent who finds a rule silly, he said, should ask to bend it rather than break it behind the parent’s back. “If trust is broken, you run the risk of losing contact with your grandkids. Is that worth it?”When a rule is broken, repair can be simpler than most parents think, Mitchell said. The parent’s job is to focus on the trust, not the treat. “I don’t care about the ice cream. I need to know that if I tell you something, it has weight when I’m not there,” he said. The grandparent’s job is a clean apology, one sentence, “without any excuses or justifications tacked on.”My sons are 20 now. They are still addicted to late nights and glued to their screens, but they no longer have to follow all the rules I set. I have made my peace with it. I am mostly just looking forward to becoming a grandfather. And ignoring every rule they set.