No, you cannot choose who you fall in love with, that previous answerer is off the mark completely. You don't look at someone and suddenly decide you're going to make yourself love them. Anyone who tries to tell you that has NEVER experienced love at all! EVER!
Hopefully no one is actually attracted to anyone sexually before they've reached puberty, if they are...it's usually due to some sort of abuse.
Now, as far as knowing what you would be attracted to once you reach sexual maturity, that's something completely different. You may have crushes on someone at a young age and not understand what that means.
I know I always had crushes on all my female little girl friends when I was prepubescent. But I didn't know what those crushes meant at all.
Later I knew I was attracted to females, but did everything I could think of to deny that I was actually a lesbian. I knew I was, even said to myself once or twice "What if anyone finds out?"
So I dated boys/guys all through high school and later on. I even married a man and had a son hoping that if I did everything "hetero" I would somehow magically transform myself into being hetero.
The truth is, you can't and don't change your sexuality. It's something hardwired and you have no control over.
Now as far as making babies is concerned, many lesbians and gay men are having, adopting and raising children. Just being gay/lesbian doesn't mean your not physiologically identical to heteros, it just means who you love is different than heteros.
And yes, we do actually LOVE our partners. Our relationships are not solely based on sex alone.