My 18 year old son has a two year old son but i knew nothing about it till about two months ago....?

My 18 year old son brought home a two year old boy about two months ago it was while he was getting his stuff ready to move for college and everything and i asked him about it and he told me he was his son. Now for that to be true he would of had to be 16 when his son was born i do not understand why he hid it from his father and i. I was extremely upset and just angry that he hid something like this. My hubby was enraged to be honest because my son was working two jobs during the summer of his Junior and Senior year and he said he was just wanting to save up money so trusting our son we didn't really Question it and i guess we should of. My hubby and i asked him who the mother was and he told us her name and then i asked her how old she was and he told me 22 which to be honest really set my hubby and i off. She signed over all her rights to the boy about three months ago he told me and now he is trying to take her to the court for Child Support. My hubby and i are not sure what to do to be honest because every time we have been trying to help him out he rejects it i want him to focus on his schooling and such but he wont or he cant i think at least with a two year old running around his apartment. How can i help my son? Why would he hide this from us? Advice?