Did she call on mobile?
if so, in future just say you’re out for the day, not at home. Or that you’re about to go out, so could leave them outside door . She doesn’t need to know if you are in or out
so, not unreasonable to say you can’t hand over to WIFE, you could have been out anyway
BUT, if KID has a key, then they can just pop in themselves and grab what they want.
AND it is unreasonable to stop your teen kids coming in if they have a key already anyway. Your home IS also their home until they are independent, which they aren’t now. Refusing to let them in to collect something, potter around or even sleep is not ok, even if you have a new partner.
If there’s a risk of that happening then you’ll need to go to neutral territory until it’s time to introduce them. Or alternately introduce them earlier but very very casually so they’re not surprised to see her there, and neither them nor her are treating it as anything significant - a bit as they would with them meeting a colleague who’d popped over to collect something, or gym buddy etc. i I don’t think it’s unreasonable though to expect that if they’re letting themselves in that they either text you a heads up before they get there, and/or give bell a quick ring before entering- that’ll give you time to adjust clothing and stop snogging .
There’s a big difference between ex wife wanting to collect something, and your children wanting access to their home whenever and for whatever , even if a tadge irritating. Boundaries related to your availability are appropriate for your ex wife, but never for your kids.