I need help. So I'm flying to Seattle this Friday to visit family, I am also flying for the first…

I need help. So I'm flying to Seattle this Friday to visit family, I am also flying for the first time with my son. I need his birth certificate so he can get by security (he is 1). I'm 17 and on the website it said I didn't need an ID since I'm under 18. I'm not sure if I need an ID or something that proves I'm his mother , can anyone help me find out what I need ? I'm flying Alaska airlines