The child said so! He knew if he could go outside and play with other kids or not.
A 5 year old's word is not often classed as reliable testimony.
The Dr. said he saw signs of neglect.
Not serious enough to call child services though, correct?
Hence, non-issue.
The child's bed was in an adjacent room with a doorway but no door anything/everything that happened in the room was clearly visible. The child could describe the activity he saw and say that it scared him and he cried but mommy was busy and wouldn't help him.
Again a 5 year old's testimony is not going to be worth much - unless the child was seen and treated by a professional therapist who might be able to testify that Mom's actions had directly harmed the child.
You would also expect Mom to testify that YOU and she had, at some point during the marriage,
also had relations with the child inadvertently present...
See above. The mother admitted it, almost proudly, in the presence of the paramours's wife. The sexual activity continued over a period of 5-6 months. There was nothing to screen the child from the activity.
And Mom is going to say that there was a curtain over the door frame, blocking the child's view/access.
No proof of wrongdoing.
Just curious. Kinda wondering what if?
If "ifs and ands were pots and pans, there'd be no need for tinkers", as my Grandfather would say.
In other words - we can sit here and speculate for days, but since a) you haven't given us a timeline (the laws can change, for one thing) and b) it's by your own words too late to do anything, the possibilities are numerous and the discussion is probably moot.
But since I'm here answering anyway....if it happened today, Mom would not face any criminal charges unless the child was found to have been neglected or abused. And even then, as primary caregiver she will generally be given at least one chance to clean up her act before custody would be taken away from her.
Again your recourse would be to file for divorce and get a decent parenting plan put in place.
Hope this puts things into perspective a bit.