New to dating as a single mom.. how do I bring it up?

I’m a single mom of a 3 year old, turning 4 soon. I’m 22 so most of the guys I meet are from my University. There’s this one guy I was interested in and he was interested too, I look super young and most people think I lie when say I have a kid LOL. Today he posted a picture with the caption saying “caption this picture” one of the comments was “when she says she has three kids” and his response was “nah, even one tbh😂😂” and I felt kind of upset. I usually don’t bring up that I have a kid right away because people at my University don’t really relate to it. I just find common topics to talk about when making friends.. how do I tell him I have a daughter without making it seem like I stalked his page?