“Last Saturday, the girls decided they wanted to go ice skating. When I dropped them off, Sara realized she had forgotten her money so I loaned her $30 to cover her admission and rental. My Venmo is xxxxx when you get a chance.”
So if you are saying what the activity was, are you assuming they didn't already know? If so, I would venmo the money but politely ask for the parent to please not drive my child to activities in the future without a heads up to me. The money is not the issue, I want to know where my kid is and what he is doing, generally.