C.
I would watch it for a day (maybe even two) if you think it's small. Wash it often and manipulate the area to help back it out as best you can. When in doubt, call your pediatrician.
When my oldest was 4.5 or 5, she picked up a fairly large sliver in her foot. Like you, we tried to extract the sliver ourselves as it was within reach. She was extremely difficult which made it impossible to have a steady hand to grab it (all while watching a 2 year old). Dad finally came home from work and didn't have any luck either. We finally had to make an "emergency call" to the pediatrician. My husband took her. She was brought in by a wheelchair (which in her eyes was the coolest thing ever), held down by my husband and a nurse while the doctor made a very slight incision and yanked it out. After a little neosporin and bandage, they were off for milkshakes in a matter of minutes. It was a very exhausting evening for all of us however it was worth every penny to have the doctor do it (even with being charged as a minor in office surgicial procedure). To this day she remembers that incident and won't even think about removing her shoes at the park again!!
