Thanks for the quick answers!! I am sorry that its taken me a while to get back on. I'd forgotten all about the fact that babies grow so darned fast... I'm always in denial about that!
The cast-on I mentioned is for the back only... and the pattern calls for acrylic baby yarn with 3.25 mm needles. I think it makes such a big bottom edge because of the decreases that give it a little gathered effect. Here is the picture they show from my circa 1970's book.