I have 2 rods in each child's closet. The top one is a bit taller so that longer, tea length, church length dresses, and jeans/pants/sets can hang without hitting the bottom rod. The short stuff goes on the bottom. Tee's, skirts, shorts, etc....they are up high enough that they don't touch the floor.
I take everything out in the Spring and again in the Fall, sort through it, have tubs that are labeled for clothes not going back in her closet and fill them up from a central location. I sit in the middle of the room with a pile of clothes in front of me and pick up, if it is too small for the next season it goes in a donate box, give to younger sib box, give to this kid and another to go to a different kid, or a huge outdoor trash can.
For the Girl: I put all Summer stuff that she can probably wear the next Summer in the long flat tubs that have rollers on the bottom and go under the beds. I keep a few tees and pants, dresses, not totally Winter weight clothes that are good for hot Fall days but mostly everything else for warm weather is gone to storage under the bed or is gone out of the house.
When I am changing from Winter to Spring I tend to leave more clothes that are for colder weather because weather can change and be too cold for hot clothes so quickly. Some of these things can be layered so that if it warms up during the day she can take off a sweat shirt or a heavy top.
I also do the same with clothes that are given that are several sizes too big. We have a couple of boxes of clothes in the bottom of the boys closet that are clothes for both kids that are for a couple of years into the future. I still go through the box at the same time I go through other clothes but I do those boxes on a different day. That way I am not running the risk of mixing up the clothes and having way more stress.
It is pretty easy to keep up with things getting too little for either of them too. I keep an orange tub in the laundry area that those things go into when they come out of the dryer. If it is too small or not liked it goes in the tub. When I sort clothes that tub is separate so that I don't mix those clothes back in the general mix.
This does not work for my friend, she forgets that there are clothes stored and when she finds them they can be years out of size. You need to find the system that works for you.