You could add a wide ruffle to the bottom of the smocked infant dresses to add inches to the length.
Firstly, you measure the width of the front and back of the smocked infant dresses. Lay the dress flat on your work surface. Measure the width of the bottom of the smocked infant clothes, flip it over, and measure the same place on the back. Add the two numbers together, add 2 inches to the total, and then double the measurement. Write the number down on a scrap of paper. Add 1 inch to the number of inches of length you would like to add to the bottom of the smocked dress. Write that number down. Cut a piece of coordinating fabric to the dimensions you have on your paper. You should have a long, skinny rectangle of fabric when done. Fold the long bottom edge of the rectangle 1/4-inch and iron. Fold the edge another 1/4-inch and iron flat. Place the strip on the sewing machine, and sew a straight stitch over the folded edge to hem. Fold the rectangle so the short sides are right-sides together. Sew the short sides together with a straight stitch.
You will now have a circle. Sew a line of stitches using a long basting stitch on the top, raw edge. Do not backstitch at the front and back of the smocked infant clothing. Leave long threads at the beginning and end of the line of stitches. Sew a second line using the same directions 1/4-inch below the first. Pull the long threads on the ends to gather the fabric. Flip the dress inside out. Work the gathers around to evenly distribute them on the fabric strip. You will need to gather it so the piece will fit around the hem of the dress. Match up a side seam of the dress with the side seam of the gathered fabric. The gathered fabric and the smocked clothes should have their right-sides facing the same way. The top raw edge of the gathered fabric will attach to the bottom hem of the dress on the inside of the dress, which is still inside out. Sew the pieces together using a straight stitch. Use 1/4-inch seam allowance. Pull the gathering threads out after you have sewn the pieces together. Flip the smocked infant dresses right-side out and the ruffle will hang from inside the dress.