One side of me, the nurse side would have ask for a glove, scooped it up, and tossed it in a waste container.
The other side of me the mom of adult children, would have said, "Nope this is a hospital and watched my child." (and I'm not saying you didn't watch your child) I know some are gonna scoff

but I'm from the school of parenting where accountability is my responsibility. Home or away, small children need to be watched. After all, this didn't occur at a daycare center.
It is impossible to say what kind of a "patch" this was, if it had any medication or if it was left by a healthcare worker or a patient. Lesson learned; You're observant, conscientious, and concerned all of these are fine qualities which will enhance your nursing career.
Opal