After having read all the way through on all of this thread, my advice is this:
1. Hire a babysitter for the child;
2. You and your husband go up into that attic and pack up everything associated with the child from babyhood, including and especially the items that were gifts;
3. Bring them with you the next time you take the child for his visitation.
Why? Because, IMO, if you give some but not all, you will have no peace. You will look small and petty even if you aren't. Because this person and these things - these things, which were used for her child, are starting to take on mythic proportions. Because they are only things.
I would not re-use the gifts given by a mother to her daughter on the birth of the child that is your stepson. I would not refuse her these items.
Yes, you have a whole bunch of good and valid reasons not to: the way she asked, the abandonment of the items years ago, the attic/looking for/packing/PITA aspect.
But the bottom line, in my opinion, is that there was a child, there is coming a child, the provenance and ownership of these items is far from clear, and the withholding - no matter how good and valid the reasons or excuses - smacks of churlishness. Sorry. It does.