How to tell my mom...?

... that my boyfriend has 2 kids? Okay, I'm 19 years old, my boyfriend is 23. He is a sous chef, so he earns a lot for his job. He has 2 kids from the same woman & they're 3 & 2 years old. I've already met them & i love them to death! They're amazing & I don't treat them any different. He's been struggling with them because of their mother. She always leave the kids at someone's house while she goes out and parties. Sometimes she'll leave them there & disappear for a couple of days. I never had an issue with her, but the stuff he tells me & shows me is ridiculous. She is my age & she acts so immature. He gets frustrated with her, and it hurts me to see him cry because he wants the best for his kids & he tries to do things for them . Since I started dating him, I helped him out with them , I made sure they were good & i made sure he was good too. Anyways, He wants to meet my mother, & I have no problem with it, just I don't know how she would feel about me being with a guy with a kid, let alone TWO kids. He really makes me happy, his kids make me happy & there's nothing that I would do in the world to change that. Just being around him & his kids really changed my perspective on how single parents struggle when it's just them . I'm still in college, so I know my mom would feel like it's "not my responsibility" to take care of them, but I feel like they give me a lot of practice for my career path & for real life situations. What can I do & how do I tell her before they meet? I truly want her to accept him for who he is, kids or no kids. It was in the past & of course, me and him don't plan on having kids anytime soon, but if it happens then it happens, but in the meantime we both are working together to make our relationship stronger. We're going on almost 4 months soon too, so I wonder if it's too early to introduce to my mother?