I have sewn for my 2 DD's (ages 8 & 9) since they started kindergarten. I sew for them using the same rules that I would use for myself. I take their measurements once a year and record them. I purchase the pattern based upon what their *actual* measurements are rather than their RTW sizes.

One of my D's is very thin and very tall. I re-use the patterns that still fit in body width but add length to them. This is very easy to do in pants, skirts and vests because the patterns have lengthening and shortening lines. Just remember not to add more than 3" of space in one place, unless the pattern only has one place to lengthen it and even then I add some space at the line and some space at the hem. So that I have changed the pattern proportionately.

I like McCalls patterns because their styling is more current. My DD's are real fashion plates. They have gotten used to being able to pick their own fabric types, colors and styles. 2-1 they will pick a McCalls pattern because it is cooler.

Since you have 3 under 5, pull-on pants and vests would be real easy to sew and if you have a serger most of it can be constructed on the serger. Vests don't necessarily have to be lined like most patterns specify. (My D's actually complained that no one else's had lining.) A pair of pants and vest can be constructed from 1 yard of fabric for these little ones!