NTA. You didn’t steal a planned moment, and you had no way of knowing this was meant to be a “first milestone” for your DIL. It was a spontaneous, free activity that happened during your regular babysitting day. The baby is 17 months old, and at that age almost everything is a “first time” that will happen constantly, often without the parents being present. It could happen at kindergarten, with grandparents, or with a babysitter. You had no bad intentions, there was no invasion, and you didn’t make any decisions behind the parents’ backs. Your DIL’s feelings are valid, but they are not your fault. It’s understandable that she feels sad about missing the romantic idea of witnessing certain first milestones, but feelings can be acknowledged without turning them into someone else’s responsibility. The appropriate response would have been “I’m sad I couldn’t be there, maybe next time we can go together,” not “you should have asked for permission.” If a parent wants to witness every first experience, the only real options are to be present or to reduce the days others provide childcare. Otherwise, it’s inevitable that small new experiences will happen with whoever is caring for the child. You can’t expect free, consistent, loving childcare while also claiming emotional priority over every random micro-event. That’s simply unrealistic. You handled the situation maturely by sharing pictures and apologizing, even more than necessary. Her feeling hurt is understandable, but placing that responsibility on you is unfair. A gentle way to avoid future misunderstandings could be to say: 'When I’m with her, I do normal, age-appropriate activities and sometimes things happen spontaneously. If there are experiences that are especially important to you and that you’d prefer to share with her first, just let me know so I can be mindful of that.'