Pants and shorts are easy, at least with elastic waists for your little ones that have no curves. I promised a few people that I would show just how easy it was and while it may have been quite a while since making that promise, here it finally is.
Pants and shorts are basically four pieces, two identical front pieces and two identical back pieces. You can find quite a few patterns for little ones that are actually two pieces, where one is a right side and one is a left side. If the side of shorts or pants is a straight line, I will combine them into one piece so that I don't have the extra seam to sew and save a bit of fabric in the process (for that you overlap the pieces so that both pieces meet where the seam allowances are).
Here are the four pieces all right side up.
First, you place one front piece to one back piece and sew the inseam. In the picture below, the wrong side of the back pieces are on top and only the bottom two pieces have been sewn together. You will read in a lot of places that you need to sew knits with a zig zag stitch or only serge. While I have serged these here, I think that a serged or zig zag stitch is only necessary on horizontal seams or the seams that have stretch (so for shorts and pants, really you only need this at the hem and waistband).
Then you take the two pieces you just sewed and place them right sides together so that the two front pieces face each other and the two back pieces also face each other.
Match the sides and sew the inseam. In the picture the front pieces are on top and the back pieces are facing each other on the bottom.
Then you flip the inseam to the inside and now you have one front piece and one back piece on top, right sides facing together and one of each on bottom.
Sew the side seams down.
Then hem the bottom and finish the waist seam and you are done.
For the waist seam, you can make a casing and thread the elastic through, or what I did here was make an elastic loop the size of my daughter's waist and zig zag it to the edge of the waistband and flip it inside and sew it down, either with a zig zag or coverstitch.