This tee is designed in 100% cotton and the cast on should be firm. If you are using a blend or another type of yarn the neckline could stretch considerably and you would need to modify the neckline.

Look for coordinating adult tee: Ruched Yoke Tee Adult

Finished Size : 21½ (23½, 26, 28, 30, 32½)“ chest circumference, to fit ages 2 (4, 6, 8, 10, 12). Tee shown measures 21½”.
Yarn Blue Sky Alpacas Skinny Cotton (100% organically grown cotton; 150 yd 137 m/65 g): #312 pear (pale green), 3 (3, 3, 4, 4, 5) skeins.
Needles Size 6 (4 mm): 24” circular (cir) and 2 double-pointed (dpn). Adjust needle size if necessary to obtain the correct gauge.
Notions Markers (m); tapestry needle.I

Gauge 20 sts and 34 rnds = 4” in St st.