Yard sale leftovers, keep or give back my finds?

So I happened to stop by a yard sale that was over and leftovers were free. It looked as though about 5 siblings or a couple siblings and spouses were running the yard sale and maybe there mother had passed away. There was a lot of old stuff.

I ended up picking up a box of jewelry boxes that held three smaller boxes. I opened one and saw it was pins of some sort so I tossed in with my stuff to look at when I got home. I had two young kids with me and groceries in the car so it was a quick stop.

Long story short I got home and looked through the boxes. The pins are old boy scout ones, another box with two sets of earings- very nice. And the third box has a ring in it like a vintage wedding one 14k marks and maybe some more engraving.

Would you return the jewelry in case it was an accident or keep it?

To return it I would probably leave a letter at the house if someone wasn't there. Saying something along the lines of I was at your yard sale the other day and found many good things and I think somethings that may have accidentally gotten given away. The yard sale was all day with lots of signage- supprising no one else noticed or found the jewelry items - nothing had marked pricing at the yard sale.

If I kept it I would probably get the ring fitted and pass down to my kids- gah am I horrible for even considering keeping it?