My 1 1/2 year old son was on my bed an took my off of him for a second to calm down my 3 week old baby an my son had gotten in my sister room where she had some thumbtacks on her bed an he was in there playing with thumb tacks im freaking out right now .... how do i know if he swallowed one or not ??
You could ask him, even at 1 1/2 if he is in pain he should be able to tell you. Otherwise your choices are to watch and wait, or to take him in for an X-ray.