I stumbled upon this fantastic fleece pajama pants tutorial and pattern via Pinterest. I tried it out to make a couple pairs of pants for Christmas gifts this year. This tutorial is so amazing because it includes a video tutorial, as well as pictures, AND the patterns for sizes to fit 18"dolls through size 6 kids. I am not the best at sewing, so I can use all the help I can get! It is super simple and straight forward.
My only warning I have for the pattern is that they run small. The picture above is the pattern for 12-24 month, and it came out perfectly. To fit my 3 year old (36 lb, 39 inches ), I had to use the 5/6 sized pattern and shorten the legs a little bit. Just a warning ;)
Once you do the first one and understand the process, they are very quick to make!