Hi Cas I’ve been thinking about this. Not to reply at all looks a bit childish (and may be perceived as game playing), but then to give in would allow him to see you as a pushover. Ignore what the kids have told you, if he wants something specific he should ask you directly. What about reply, state that you thought he’d bought everything when he moved out, but ask if he wants anything in particular. Are you sure it’s for him and not for OW or her child? It does seem to be an odd thing to ask for. Sounds from what the kids said it’s nothing of value so probably not worth getting in a lather about.
My view is that if it’s not important there’s no need to sweat over it. Is he going to want to spend more time with you if you make a big deal and fuss about every little thing? 
