Tightness was a problem for me at first, but I can tell you a nice hard penis stretches it way better than any old hard plastic dilator! My largest dilator (not counting my boyfriend lol) is 1.5 inches diameter. I will never talk about my "depth" as it just sounds too much like guys measuring their penises. But I'll say my boyfriend who is somewhat well endowed has no problems, and he, like most guys, actually prefers a tight vagina to "throwing a sausage down a hallway".
I don't know about a baby's head, but the skin is pliable and it can stretch. I also sometimes use estradiol cream internally as it has many benefits, one of them to keep the skin soft and stretchy. Also pure lanolin cream (like breastfeeding mothers use on their nipples) around the outside can do the same thing.
