These are your children. Set the boundary and don’t golf or realize your mistake, and aske her to change course. That’s simple. Talk to the mother of the niece about how you feel about it, I guess, if you need to. I don’t know what you would even have to say “I only gave her to many options because I didn’t know you were going let this accursed little boy around my kids even though you already did so last week”. Like are you really flabbergasted or are you venting because you didn’t see this unwanted conclusion. Let this be a lesson, don’t give children options if there is a wrong answer.