Deciding whether to intervene in a minor friendship conflict

My child came home upset because two friends planned a game without inviting them. They want me to message the other parents. I know how much it hurts, but one awkward afternoon isn't necessarily a pattern of exclusion, and adults intervening can make school friendships even more complicated. I'm leaning toward listening, helping my child decide what to say tomorrow, and watching whether it keeps happening. Where do you draw the line between coaching and stepping in?