Aww don't worry Rhonda, kids do stuff like that all the time, it totally doesn't mean you're a bad mommy! I stepped out of Owens sight for like..less then 60 seconds when we were visiting family and he was a yr old..2 other people were in the room and he still managed to swallow 2 of my Brother in laws A.D.D pills! I was freaking out but the poisen control people and the doctor both assured me they hear way worse on a normal bases.
My friends 2 yr old son got his hands on a BB gun this past weekend and shot himself in the finger

Kids are just sneaky.
It sounds to me like he stuck it in his diaper though, and even if he did swallow it, at least he already passed it