Choose a piece of oilcloth fabric that will be appealing to your child. Fold the fabric in half to form a square.
Measure and mark a hole for the neck on the fold. The hole should be centered along the fold and should be wide enough to slip over you child's head. Cut it out using pinking shears.
Determine how long and wide the smock should be by holding the fabric up to your child or using an article of his clothing as a pattern. Mark the length and width with a pencil and trim the bottom edges and both sides at your marks using pinking shears.
Start on one side of the smock at the shoulder and work downwards. Measure and make a mark every 4 inches. Repeat on the opposite side.
Punch holes at the marks about 3/4 inch inwards from the edge of the seam. Line the fabric up so as you punch, the hole goes through both the front and back layers of fabric.
Measure and cut as many 8-inch strips of ribbon as the number of holes you punched. The number of holes will vary as the lengths of different smocks will be different depending on the height of the child.
Pull the smock over your child's head. Secure the smock by tying a ribbon through each of the punched holes.