He could really go either way. Sure, he likes kids and loves his big family, but growing up he saw how he and his siblings drove his parents nuts and thought a couple of times “Is that something I really need in my life?”
Then he joined voltron and just accepted that kids were not happening for him, no family of his own. He’d fight his life away in space and if he ever made it back home then it would probably be too late for him. He’d just recede into his own family and become crazy uncle Lance with the war stories and he’s not super ok with that but it doesn’t tear him up inside.
And then, he found out Keith wanted kids. Keith was alone for a large portion of his life and while he would never admit it outloud to anyone, Lance can see it in the way he stares and smiles at the children they save. In the way he looks longingly at the families they reunite. In the way Keith asks him about his huge family back home with tons of kids running around and his eyes soften at the stories. It’s dark in the room they now share, wrapped up in eachothers arms and Lance asks the question he already knows the answer to.
“Do you want kids?”
Keith blushes and sputters and avoids eye contact but somewhere in the middle of all that nonsense he mutters an “I guess” and he’s so embarrassed by it he turns away from Lance and he spoons him, resting his head in between Keith’s neck and shoulder. And then he hears a small, terrified whisper in the dark.