3-year-old "touching" other children in Daycare

I went to pick up my 3 year old son from daycare today, and the director pulled me aside and told me that he has a problem touching girls in his class.  She said that the little girls told the teacher that he "touched their peepee" and when the teacher told him that was not appropriate he told her that he didn't have to listen to her.  The daycare director told me that I should take him home and reinforce the good-touch-bad-touch rules and let him know that is not appropriate behavior.
I asked my son about it on the way home, and he insists that he didn't touch anybody.  I tried to make it clear that the bathing suit area is private and he shouldn't touch ANYONE in that area and NO ONE should touch his either.  He knows, I think, that anyone who does this can get in bad trouble and hurt people. (that's exactly how I put it) He still insists that he hasn't touched anyone's peepee and got quite upset when I continued to question him.  I don't want to push him or scare him or make him feel guilty or bad so I let it drop for tonight.
Now, I love this daycare, I actually attended the same daycare as a child.  And the director has always been like a grandmother to my kids, but I am kinda getting the feeling that this particular teacher (who had problems with my older son when he was in her class) might have it out for him.  She seems to have something to say about my son's bad behavior everytime I pick him up.  I have never heard of him doing this in his previous classes, and he previous teachers have loved him.  He is a hyper kid and probably has ADHD, so maybe she just can't handle him.  I don't want to start any conflicts, but I am feeling kind of persecuted.  How worried should I be that my son could be molesting other children? How do I handle this situation?

[RockRose]

I would investigate this further.  It would be odd that if he touched several girl's genitals they would all describe it as their "peepee", which is actually  urine.  It's very hard for me to believe that several girls voluntarily said he touched their "peepee",  uncoached.   If he's going around touching the girl's genitals,  why didn't the teacher actually witness this?

Can you get him into a different class?  Considering your other son had a bad time at this daycare,  I would consider looking elsewhere.