The pattern, available from The Hooker in Me, comes in two sizes, 0-3 months and 3-6 months. The largest size comes out at about 4 and a quarter inches long, when crocheted loosely with a big hook. You might be able to make them bigger than me though, since I crochet really tightly (I now have a really bad joke about skinflint hookers in my mind, but I won't share).
I had hoped to make these for VV, but sady he's got kipper feet like his mother and at six months is way too big for these. Not to worry though, I've got plenty of newborns to make for in the next few months. I think I'll make a pair for each one and add a couple of other gifts too. They only take about an hour each to make, so they're perfect for running up in front of the TV of a cold wintery evening.