6 year old boy asked my son to pull his pants down....

I'm a divorced woman with a 3 year old boy and I'm dating a divorced man who has 3 boys of his own (6,9, & 11 y.o.).  We spend weekends together with all the boys but this past weekend something alarming happened.  The 6 year old boy and my 3 year old boy were playing upstairs and at some point in time the older boy asked my son to pull his pants and underwear down.  My son has been taught (after a traumatic situation this past year) to NEVER take his clothes off for anyone but his mommy, daddy, or grandparents.  And I've also taught him that he has private parts and we make him clean those places and only in certain circumstances (seeing the doctor) can ANYONE touch them.  Luckily my son, once asked to pull his pants down, came running down the stairs as fast as possible to tell me that he said "Mommy, I said NO, I will NOT pull my pants down to (this boys name here)!"  I was confused and the other boy INSTANTLY said "he's lying, I did not!".  Of course I freaked out, though I wished I hadn't have and demanded to know what was going on.  Being that my son was "groomed" by his babysitters husband and we've been through this before but with an adult, all I could think of is that it happened again.  My boyfriend and I talked to his son about it and he swears that no one hurt him in any way but that a boy on the playground asked him to pull his pants down so he asked my son the same thing.  I asked if he pulled his pants down for the little boy on the playground and he said no but he wasn't sure WHY he wanted my 3 year old to do it.  

I'm extremely concerned that something has happened to the 6 year old and I'm very concerned that I'm putting my child in a bad situation.  Does this behavior sound "normal"?  Because my boyfriends ex-wife seems to think it's just boys being boys.  This is my first child and it seems VERY strange to me.  PLEASE HELP!!!  What should I do and am I overreacting in this situation???  Any advise is helpful...Thank you!

[treazzure007]

Being alarmed is normal.  You should be.  I dont think that any 6 year old is a danger.  That's still so young.  This 6 year old may be going through a stage where he's curious about anatomy or, of course, something and someone else can be the cause of a sexual awakening in the boy.  It's best if you keep your eyes and senses keen to him and his brothers.  Keep your son with you and in your sight always regardless.