Years ago, your in-laws may have realized they had done something terrible or it was a mistake, so I have a few questions that you should consider before deciding what to say to them. First, do you think they are OK? It’s pretty weird to be signing checks that are for something you ostensibly need to pay for over to a charity, right? Do you think your husband’s parents could be being taken advantage of in some way? Are they starting mentally?
If yes, this is a health and safety issue that your husband needs to address with them. Now, say they are mentally well. Are your in-laws supportive of and kind to your child? To me, this is the biggest question: Not whether they sent your check to a hateful cause, but do they treat you and your child with love and respect?
If they treat you both lovingly and respectfully today, I think you should let it go. You don’t have all the information for one thing, and for another, the statute of limitations has passed on that check. But if your in-laws are not kind or supportive towards their grandchild – a conversation is warranted – not about the donation but about that treatment which impacts your child today.
That’s a conversation your husband should have with his parents, making it clear that if they want to remain in your lives and continue having family reunions, they will need to accept you. As for the check well once you send someone money it belongs to them. While you can definitely ask that specific check doesn’t go towards an anti-trans cause – once the money goes into the bank each individual dollar isn’t marked where it can or cannot go.
If your mystery is really getting to you though, I suggest just paying for these trips yourself, or accepting that “your” money in this case is not yours at all. If you want to know more about what happened – have your husband casually ask his parents: “Hey did one time donate some of our money towards a Christian college?” Then at least you’d know.
Good luck!