My son will be 1 in a month and he runs a bit bigger than your average babe. I order him a 12-18 month because of this fact and the shirt fits perfectly. I wouldn't say you need to size up because he's just bigger than the average, so it's really true to size. Great quality, came with the tag from Children's Place that had the item marked at $14.95. Can't beat 50% off! We tried this on with a pair of suspender shorts that we ordered our son from Bailey's Blossoms for our wedding at the end of August and oh my goodness it's adorable! Happy with the product for sure!

P.S. The color is white, and I was nervous because the groomsmen are wearing ivory but it will work fine because while it's white, it's not a bright, blue toned white. Its a nice white linen type top. Very cute.