Measure the size of the toddler's outfit to determine the length of the snap tape. Measure that distance on the snap tape and mark the cut location. Cut two pieces of tape to size with a pair of scissors.
Match the two pieces to verify they are the proper length. One piece of snap tape will be installed on each side of the outfit so one side can snap into the other.
Set the tape at the proper location on the outfit and pin it in place on each edge of the garment with dressmaker pins. Sew the snap tape in place with a sewing machine.
Snap the two sides of the tape together. Verify they fit together properly and are sewn on tight enough. Grip the snap tape near the buttons and pull up firmly to separate the two sides.