Some of my children are very "hard-to-fit." I've spent a lot of my mothering years taking hems up and letting hems out, of adding elastic to waistbands or making darts in a seam. I find myself pressed at times with quickly growing children. I would tend to neglect my mending pile, if I weren't nagged by the thought my children will outgrow the clothes without ever having worn them, if I don't get them mended. The clothing is usually in the pile precisely because the child needs it, so while guilt is not a great motivator, in this case it works. I do like to make mending or altering as painless as possible, however, so here are a couple of links for some shortcuts that I've found. They really are easy, and they really do work well.
I hemmed these jeans for Julia by hand, then because I had time left over I added some freehand embroidery. She was tickled pink, red, and yellow. :)