I've always gone down just one size, and that has worked for me, but best to try things on.
kids clothes are very small - ours tend to say 1-2 on them, there's will just say 2, so it's not from 2, it's until 2 if that makes any sense? I bought my dd a few outfits when she was 1 and they hardly lasted anytime at all, I couldn't work it out until I compared the measurements of the garments
Bev