I have a small stray cat that had kittens, how do I know if they're alive?

I live in the country and 3 wild cats showed up in November. One is female and very small. Finally after six months she let me touch her. Now she is very affectionate. She just had kittens 3 days ago. I can't find them. How do I know if she is nursing them or if they are even alive. Her tits aren't very big. And the other two cats are male. I'm afraid they killed them.

I have a small stray cat that had kittens, how do I know if they're alive?