Remember ex's son's birthday, for sure

You cannot control how this gesture is construed, nor should you spend too much time worrying about it.

If you want to give this boy a gift, don't send cash, send him an age-appropriate book. Many boys don't have enough books in their lives.

Put this event in the category of other non-necessary spending (e.g., golfing weekends or bird-watching trips); in my view, if you can afford it and your wife really wants to attend, you should.