Clothing four children inexpensively is not something that can be done without planning and organization. (So much of what frugality can accomplish is impossible without organization.)
Here is a picture of some of the hand-me-downs I've saved for the kids. (Yes, I said some.) The kids range in age from 8 months to 8 years old - that's quite a bit of clothing to hold onto! We have a large-ish garage (2 1/2 car) with shelving covering one side. Fully 1/3 of it is taken up by clothing and shoes, boxed by gender and size. We have a few boxes in the attic of the house. Coats, gloves, hats and scarves are in a big rubbermaid tote in the basement.I've (mostly) used copy paper boxes, labeled, and put in order by size from left to right. Because I have such a large volume of clothing to choose from, I only save items that 1. I like 2. are unstained 3. are in good repair. I don't throw away clothing that I've chosen not to pass down. Instead, I either save it for our annual garage sale (another box in the garage!), or, if it's unsalvageable, I tear it up to use for cleaning rags. To repeat myself, because this point cannot be overstated, I only keep clothing that looks like it hasn't been passed down! I don't want my children to feel shabby, and having a large-ish family, it's important to me that my children look well-cared-for.
Saving clothes to pass down is only ONE part of the clothing system that I use. Getting the clothes for the oldest child to pass down is another matter - and being the cheapskate that I am, I do not pay full retail!
Please forgive the blurry picture - Gracie wouldn't let me put her down. (I know, you're surprised!)
This is the keystone of the system - the hand-me-up box. I got the name from a couple of friends, and the idea from The Tightwad Gazette. When I'm out garage sale-ing, I keep a sharp eye out for clothing that is a size ahead of what the oldest child is currently wearing. (For the boys, Adam wears an 8 right now. For girls, Grace is currently in 18 months.) For younger children, I have to keep the season in mind, too. I know the bigger sizes (starting at about 4 or 5) will be worn for a full year, so I can buy Adam's clothes for summer or winter wear. But for Gracie, it's another matter. I have to make my best guess about what size she'll be in the spring, when she'll need warm-weather clothes. But at garage sale prices, I can afford to make a few mistakes. I can always choose to sell wrong-season clothes at our annual garage sale, or I can keep them, awaiting the next child who might "line up" with that size in the right season.
In any case, when I have enough of the next upcoming size in the hand-me-up box, I "break out" a new box, label it with size and gender, and put it on the shelf. Grace has a full box of 18 month winter clothes that she hasn't worn yet. In the hand-me-up box, Adam has some size 8 jeans (he was a 7 last winter), tees, and sweatshirts. He also has some size 10 items waiting. There are some larger sized (2T-4T) items in there for Grace, too - things that were so inexpensive and so cute that I couldn't pass them up.
When each season changes, I "go shopping in the garage" and pull out clothes for everyone, putting away out of season clothes. The boys get a big kick out of getting a whole new wardrobe all at once, and I LOVE not spending a ton of money on clothing. As a side benefit, the kids closets are rarely crowded with outgrown clothes, since I can just rotate them out to the garage mid-season, and rotate in clothes in a larger size.
In the future, I'd like to have a clothing inventory. I'm thinking a spiral notebook, with one size/gender on each page, and a brief list of clothing, so I know if I'm short on 3T jeans, or size 6 sweatshirts. But that will have to wait until I clear my craft table and paint the bedroom.