Can police question you on a felony, then six month later charge you with a misdemenor?

About 6 months ago i was going thru a divorce and custody battle for my two year old son colten. the mother had left us in april of 2010 and didnt contact us for 2 months. i went and filed all proper paperwork for custody and when court came dispite everything they still gave her 50\50 custody. so over the summer the mother called cps on me once a week for 6 weeks in a row (all of which were unfounded) then july came and the mother had bounced from place to place and the place she was now staying was infested with bedbugs. my son was comming home with bites everytime he went with her and i told cps but nothing was ever done. so on my sons birthday august 3rd the mother showed up to pick my son up for her half of the day (12pm to 6pm, by order of family court that she was to get him for half the day on his b day) she came alone and i knew she had no licence so i called the sherriff. (come to find out it was a trick cause her licenced driver was down the road) but anyways a sherriff arived and also a state trooper. they asked me if i was going to let my son go w his mother or not and i said as long as there is a licenced driver. so heres why im asking the question. when i went to pick up my son later that night no one answered the door. i went to the local police to retrive my son. he met me at the house and went to her door to see if she would release him. she told the officer no cause she claimed i had punched my son in they eye and called cps again and went to a detective. needless to say i didnt get my son the night of his b day to share w my family. the detective had me come in the next day to question me about his swollen eye i told him they were bedbug bites (and you could see that in the pic) i also told him that during the exchange of my son a sherriff and a state trooper were present and they didnt see any swollen eye (which they are mandated by the state to report if they see) at that time the investagator said im not going to arrest you i dont think you hit him. so i asked if he could charge them with false statement, and he said was too hard to prove. so i left thinking good the law finally worked. at the same time the mother had went to court and lied to get an order of protection so i couldnt see my son saying that the police had charged me with endangering the welfare of a child. so with no research the court granted her the order, then transfered the case to the county in which she lived. i didnt get a new court date for a month so did not see my son that whole time. when i finally did go to court i explained to the new judge that she had lied to get the order of protection and then instead of dropping it he modified it so i could have my son. so custody was back to 50\50 except now i had a modified order of protection on my son. about a week later it took a turn for the good i opened the post star (our local news paper) and saw a artical. the headline read bedbug infestation in glens falls home. i reconized the person in the pic emediatly, it was the lady my sons mother was living with. unreal they were subjecting my son to sleep in a nasty house infested w bedbugs. i went straight to the court and put in an order to show cause saying it was unsafe for my son to be there. the judge granted me physical custody on the spot. she was granted daytime parenting time but didnt call or show for any and ive been keeping him safe since. so heres the thing six months go buy and were doing fine, i get woken up to a call from the investagator saying to come in that he was going to charge me with a misdemenor for the eye bruse six months ago, said he got new information which was a statement from a new friend of hers she was living with. i said your kidding right? he said no. i told him ive had my child for 6 months. i also explained again that it was impossible due to the sherriff and state trooper being there for the transfer that day and them having to report something like that if it was there. so now i have to go to court when all the info was there saying that this is not the way it happened.