'Some day.' Turtle and Theo had decided against having children because of the possibility of inheriting Chris's disease. 'If it's a boy we'll name him Sandy, and if it's a girl, well, I guess we can name her Sandy, too.' (30.27)
This is a moving description of what love is and what family can mean. Even though Turtle and Theo would like to have kids, they've decided not to just in case their kid gets the same disease Chris has. That's just a "possibility," not a guarantee, but for Turtle and Theo it's enough. They'll make a family without children in it. (On a side note, their decision raises interesting questions about whether Turtle might be relieved to not have to be a mother, considering the role model she had to work with.) Even though they've decided this, though, Turtle lies about it to give Sandy comfort when he's actually dying. Sometimes lying can be love, too.