Girlfriend has a hidden son?

I have been with my girlfriend in total of four years. I knew she had one son who was around the age of 17 and a daughter at the time who is around the age of seven. They have separate fathers. Both of the sons here have the same father. We have lived together two years now. I seen a piece of mail that was clearly hidden. It said support court, and it drew my attention. I get it not my business, however, not knowing anything about Support or never hearing about it from her to my attention so I looked. She has a date coming up to cancel Support as the youngest child is now 21 she has said nothing to me about any court dates or that she even went to the courthouse and filed. She’s never disclosed that information. It’s not really my business anyways. A few months ago a family member had passed away. I noticed a grandchild listed with the same last name of her son that I am aware of. he also showed up to the funeral. I am not involved in her family yet as there were some personal things she was tending to and dissolving a previous relationship and with a family member being sick she didn’t want to create any issues. so I don’t truly know everybody only some know who I am. When I seen this name listed in the obituary, I asked and it got brushed off as her ex’s girlfriend after her. The same child is now listed in what I seen in that piece of mail as being her child. He would be 27 years old and since I’ve known her, there is not one shred of evidence of him being in her life or her in his. It looks like she was in high school when she had him. it was very clear. This kid has had family involvement over the years, but she has never disclosed anything about him to me. I’m really unsure how to bring this up or how to confront the situation as I did see something that wasn’t mine. it doesn’t feel like there’s transparency or communication which is what prompted me to look. I think anybody would’ve looked at the document. I’m looking for the good the bad and the ugly.

Updates
+1 y
I do want to add that there has been no shot of evidence, not even a picture that is appeared anywhere in the four years I’ve known him. It comes across that something along time ago, possibly happened and there’s a lack of a relationship. So I get that could be difficult. However, what the hell.
Girlfriend has a hidden son?
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