Last week, I talked about saving money on groceries when you're short on time. The next biggest expense for most of us is clothing (outside of housing and car expenses).
The BEST way to save money on clothes is to go to a thrift store or consignment store. Even better is to go to these places when they're having a "bag" sale where everything you can fit into a bag they give you is only $5 (or another fixed price). You can save even more money if you're willing to go to garage sales.
Let's assume, though, that you don't have extra time. You need to go into a store, look at the shirts, find one that fits & go. For the best, most immediate selection year-round, I would recommend a consignment store. They are the place where you're most likely to find clean, in-style clothes in nearly any size just as you would in a "regular" store. If you have a little more time, you can get even better deals at some thrift stores. (I don't usually bother with garage sales because I don't have the time.)
I know some people prefer new only. You'll find better deals if you'll expand your horizons & be willing to consider consignment stores, but you can still save money buying new.
There are two ways to save money buying new clothes. Both do involve a watching & waiting so you would be wise to try & plan ahead clothing-wise. The same principal regarding groceries applies here too. Find what you want on sale. Every item of clothing goes on sale at one point or another. Find your favorite store (or stores)...mine is Target..and watch their sale ads. Buy what you need when it goes on sale, but try to think ahead. If your son is now wearing a 3T & there's a great sale on jeans, then buy a pair (or 2) in 4T & 5T also so you'll have what you need when you need it without having to rush out & buy (at full-price) right then.
The second (and best) way to buy new is to buy on clearance. However, this DOES take more time than just walking in & buying what you need. What you CAN do, though, is look at the clearance items when you're already in the store. If there's something you know you need or will need in the future then pick it up. Most stores eventually take their clearance down to 75% or 80% off, but the lower you go, the less they have. As a result, if it's something you need, then you might need to buy it at 50% or even 30% off to ensure you get what you need before it's gone.
And again, don't stress what someone else is able to save. If you want to eventually have those savings, FANTASTIC! Start where you are, though, and build up to it when you are ready.
Above all, remember, that ANYTHING is better than full-price!