The one problem I've found with this pattern is that the neckline is rather small and it won't actually go over many babies' heads. This one is 18mth - 2 years in size, but there's no way it will fit over a child's head of that age...
...so, what I think I'll do is cut a slit at the back and sew a button and loop. I think I'll do that for each tunic from now on.