If you should decide to make the BSJ, you can first take a look at thousands of them (over 3000 to date), in all colors and yarn types on Flickr, right here.
You will help yourself immensely, once you have purchased the book and own the highly copyrighted pattern, by downloading and printing these Baby Surprise Jacket Notes by Dawn Adcock. There's potentially a lot of math and a lot of counting in this sweater, all made much easier if you keep Dawn's notes on a clipboard in front of you.
There is an extremely helpful Knit Wiki article containing photos with arrows (helpful with placement of stripes), lots of notes, some variations, and a little chart about gauge and size that will allow you some control over your finished product. The original one-size pattern is made for a baby; this chart will give you some guidance in case you are knitting for an older child.
I wanted my sweater to fit a toddler with a 22" chest, but thought it should be a little bit big so it would still fit by the time I sent it. I worked out the gauge, actually knitting several samples (highly unusual for me!). I ended up using size 10 needles, figuring if the sweater were a little too big, my granddaughter would grow into it. However, my finished sweater will probably fit her sister, who is in 3rd grade. Perhaps it was the cotton yarn I used--not much spring to it.
So, I am ready to try again, using smaller needles and more elastic yarn. It's a fascinating pattern and I can't wait to apply what I've learned so far. We'll see what happens.