SIL tells nephew Im just a kid

Im 19 years old, with a toddler and a baby on the way. Ive been with my husband for 3.5 years. My sister in law is 26, I sometimes watch her son who is 7. He was over the other day and told me that his mom says Im only 19 and that makes me a kid so hes not going to listen to me. I asked her about it and she says its true Im still an irresponsible child, but that makes no sense considering her last boyfriend is the same age as me and they dated for 4 years? Im pretty upset that she sees me that way, I've never gotten a ticket or really even broken a law. Just needed to vent I guess

Yeah she started dating him when he was 15 but since shes a woman the police didn't take it seriously when my husband reported it