First through third grade are pretty uneventful--school field trips, plays, reading, writing and math. As far as clothing, you will want to start buying cargo shorts for your sons. They will come home with all sorts of stuff they find on the playground. When you hear that distinct rattling in your dryer, you'll know you forgot to check his pockets for rocks again! If you son participates in sports like soccer, baseball, basketball or lacrosse, you will want to buy them shirts with an athletic fit from manufacturers like Wes & Willy or Mulberribush. An athletic fit allows them room to throw a ball, swing a bat or lacrosse stick. Boys hate clothes that are too tight!
Now, girls are a different story. They'll get on a kick of either always wearing a dress, or NEVER wanting to wear one. I had three daughters and once they discovered jeans, it was hard to get them to wear anything else. Either way, your son or daughter will begin to reveal more of their personalities during this time. Cargo pants and shorts are must haves for boys. So are cool tee shirts and shoes. My youngest grandson loves the shoes that light up when he walks. Girls have so many more choices--skirts, skorts, shorts, carpi's, leggings, pants, and dresses. Oh, an FYI regarding size 6X: This is basically a half size between 6 and 7. This in-between size gives them a little extra tummy and hip room.
I find most children in elementary school do best with full elastic waist garments. If your child is slender, the elastic stops at the waist so they're not tugging at their pants all day. If you child has a tummy, it allows plenty of stretch so they'll be comfortable. I don't know who invented the adjustable waist tabs, but in my opinion they are genius! Brands like Polo, Hartstrings, Kitestring, and E-land offer adjustable waists.
In my final segment, I will talk about 7-14 size range. This is often referred to as "tween" sizing. Tweens have a lot of buying power and influence in today's retail market. Be prepared!