They are perfect for when it's cold outside but not snowy and wet. They don't really keep any wetness out (it's just yarn) but they definitely keep the boy-o nice and toasty warm for some outdoors fun, and they're much less bulky and restrictive than traditional snow pants are.
There are many different patterns available for these pants. We searched Ravelry until we found one we liked, and used that one. You'll need a login name, but it's free to use! If you don't happen to know an able and willing knitter, there are also many stores on Etsy selling them as well.
Every little should have a pair of these adorable Monster Bum pants--because let's face it, sometimes our toddlers really *are* monsters and these pants are a great way to keep mama smiling all day!