1 skein of Wool-Ease Thick and Quick will make you 3 mitts, so 2 skeins make 3 pairs of mittens for less than $20. You really can't beat that for a warm kids mitten!
I was frustrated at the lack of mittens that were durable, thick/warm and large enough for my 7 year old son. It seems like all the mittens at the store fit him at 5 and 6 years old... and now it's hard to find the "L" or "XL" size. I located a pattern for seed stitch mittens online and modified it to fit my 7 year old son. It would fit a 7 year old through a small woman's hand (fits me, but much more snugly). My son wears them with a thin, stretchy finger glove underneath & it's the warmest combination we've found yet for digging in the snow!