I was in the same situation about 3 years ago. I got bankers boxes that were sturdy and had lids and I labeled them by size and kind of garments - for instance, Boys, Size 3T, Tops. Then I took the clothes we had and chose the best pieces from those to fill the boxes. Once the box was full, everything else was gotten rid of.
That leaves quite a bit of clothes when you are dealing with little sizes, so it may actually be too much if you are really trying to cut down.
It worked for us though because we had an attic to store them in. They were put away stacked by size, easy to grab when necessary.
When we had our last baby, a son, I got rid of 17 boxes of girls' baby clothes because this one is our last little one. I didn't realize how much I actually had until I sorted into the boxes. Before that, everything had been in bags and just been tossed into the attic unorganized and difficult to ever use.
HTH!