Should I buy ski socks a size up so my child can grow into them?

Absolutely not. This is the most common mistake parents make with kids' ski socks. In regular shoes, a slightly large sock is harmless. In a ski boot, excess material creates folds and wrinkles that press into the skin with every turn, causing painful pressure points and hot spots. Buy the size that fits right now, even if it only lasts one season. The cost of replacing socks annually is far less than the cost of ski days ruined by uncomfortable feet.