A quick pair of pants to make for baby or toddler using the sleeves of a long sleeve tee shirt. The bum panel allows extra room for the diaper bum, and can be made even roomier for the cloth diaper set. 
You need a long sleeve tee that has already finished its tour of duty in your closet for the pant legs and front portion (I used a ladies L). The sleeve seams will form the leg seams of the pants and the wrist openings will become the ankle openings. Additional fabric will be needed for the bum panel, from either the same tee, another tee, or any lightweight knit fabric. You will also need some ½” elastic for the waistband.
Begin with measuring the wee one from ankle to waist. Add 2” to this measurement for the pant’s waistband.
Measure from ankle to crotch. Add ¼” to this measurement for a seam allowance.
Measure waist. Subtract 3” for waistband elastic.
Take the long sleeve tee and cut the sleeves straight across at the longer measurement mark (ankle to waist). Next, cut off the seam from the shirt above the shorter measurement mark (ankle to crotch). This will give you two pant legs, with the shirt seams becoming the leg seams.
Turn one pant leg inside out. Insert the right side out pant leg into the wrong side out pant leg (they will be end up right sides together and seams aligned).
Sew one half of the pants opening, from waistline to crotch (where the existing shirt seams are). 
Lay the pants down with the unsewn half of the pants opening (the bum area) up. Cut from the crotch (but careful not to cut your newly sewn seam) to the waistband in a wonky wedge shape (sorry for the tech jargon ;D). This is where you are going to add extra room and sew in the bum panel.
Use the cut wonky wedge as a guide to cut a wider wonky edge, a.k.a., the bum panel. Place the longer straight edge of the wedge on a folded edge of the bum panel fabric. 
Open up the pants wrong sides out. Align the mid point of the bum panel with the leg seams (right sides together). Pin in the bum panel. To avoid awkwardly stretching the panel while sewing, sew the panel in by beginning at the crotch and stitching towards to the waist (repeat for other side). 
Fold the waistband down 1” and stitch to create a casing for the waistband elastic, leaving about 1” open to insert the elastic. Thread the elastic through and sew elastic closed. Finish the casing seam.
That should do ‘er. The only thing left is to embellish your baby’s butt. I used a no-sew bonding paper to attach my appliqué, but, really, anything that will be comfortable for baby is fair game. Have fun with your happy bum pants :)
Oh, wait! Whaddya think of the fancy smancy illustrations? Good? Clear? Or are they more confusing than photos?
Measure from ankle to crotch. Add ¼” to this measurement for a seam allowance.
Measure waist. Subtract 3” for waistband elastic.
Take the long sleeve tee and cut the sleeves straight across at the longer measurement mark (ankle to waist). Next, cut off the seam from the shirt above the shorter measurement mark (ankle to crotch). This will give you two pant legs, with the shirt seams becoming the leg seams.
Turn one pant leg inside out. Insert the right side out pant leg into the wrong side out pant leg (they will be end up right sides together and seams aligned).Sew one half of the pants opening, from waistline to crotch (where the existing shirt seams are). Lay the pants down with the unsewn half of the pants opening (the bum area) up. Cut from the crotch (but careful not to cut your newly sewn seam) to the waistband in a wonky wedge shape (sorry for the tech jargon ;D). This is where you are going to add extra room and sew in the bum panel. Use the cut wonky wedge as a guide to cut a wider wonky edge, a.k.a., the bum panel. Place the longer straight edge of the wedge on a folded edge of the bum panel fabric. Open up the pants wrong sides out. Align the mid point of the bum panel with the leg seams (right sides together). Pin in the bum panel. To avoid awkwardly stretching the panel while sewing, sew the panel in by beginning at the crotch and stitching towards to the waist (repeat for other side). Fold the waistband down 1” and stitch to create a casing for the waistband elastic, leaving about 1” open to insert the elastic. Thread the elastic through and sew elastic closed. Finish the casing seam.That should do ‘er. The only thing left is to embellish your baby’s butt. I used a no-sew bonding paper to attach my appliqué, but, really, anything that will be comfortable for baby is fair game. Have fun with your happy bum pants :)
Oh, wait! Whaddya think of the fancy smancy illustrations? Good? Clear? Or are they more confusing than photos? **********************************************************
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