The very talented Dana from Made has a bevy of free tutorials on her blog. I recently made her Knee Pad Pants for Josiah who is just starting to take consistent steps but still crawling a LOT. We have gone through about 7-8 pairs of trousers/leggings/trackies etc... of course he starts walking when I finally make these pants.
I ended up tracing my pant pattern from from a pair of Josiah's trackie pants and did something I never do, made a trial pair in some old daggy material (I'm a "rush in and sew, ask questions later"- kind of girl)! I followed Dana's directions for the trial pair and they worked out great. These are a little long for him even though I trimmed them but they fit nicely and I like the frayed look around the knee pads - I sewed around the knee pad three times, then did half a dozen lines horizontally. What a cutie pie, he is now sixteen months old. I recommend the pattern and think it is great for a sewer of any ability.