You can convert your daughter's hand-me-down dress into a jumpsuit for her little brother. Some clothing themes and colours work equally well for a little boy or a little girl. Blue, green and yellow are great colours for both boys and girls. Clothes with a nautical theme and some animal decorations also work well for either sex. You can add a crotch to a girl's straight dress to make it a jumpsuit.
Put the dress on the child and pin the front of the dress to the back of the dress with safety pins, marking the location of the new crotch. The pins should form an upside-down "U" shape. You will have to unpin a pullover dress to take it off the child, so be sure to mark the crotch placement on both the front and back.
Mark a cutting line 1 inch below the crotch you pinned into the fabric on both the front and back of the dress. Cut along these lines.
Fold up 1/2 inch along the crotch on the back of the dress. Separate the two sides of the snap tape. Pin the piece of snap tape with the knobs along the folded edge on the right side of the fabric, aligning the edge of the tape with the fold. Turn under 1/2 inch on each end of the tape. Using a zipper-foot, sew along all four sides of the snap tape.
Fold in 1/2 inch along the crotch on the front of the dress. Pin the other piece of snap tape along the folded edge on the wrong side of the fabric. Place the edge of the tape 1/8 inch away from the fold, so that it does not show when the garment is snapped. Turn under 1/2 inch on each end of the tape. Using a zipper-foot, sew along all four sides of the snap tape.
Pull the jumpsuit over the child's head and snap up the crotch.
If the dress flairs out at the bottom, cut the sides of the dress with less of an angle and resew the side seams. If the dress has a zipper deep enough, you can sew the crotch seam closed instead of using snap tape, but snap tape will be more convenient for a child still in diapers. Add a snap crotch to turn a long teeshirt into a jumpsuit.