You will need stitch holders.

Note- sleeves are worked sideways, from the top point, increasing to the cuff, then eventually decreasing back to the top again.

Finished measurements:
Chest circumference: 30.25( 31.25, 32, 32.75, 34)“ 77(79, 81, 83, 86) cm
Finished length: 15.5( 16, 17, 17.75, 18.5)” 39( 41, 43, 45, 47) cm
Sleeve length: 10.25( 11, 11.75, 12.5, 13.5)“ 26(28, 30, 32, 34) cm

Yarn used
Sirdar Snuggly Replay
On Girl
A. 106 Blast Off Berry - 4(4, 4, 5, 5) balls
B. 109 Full of Beans - 1 ball for all sizes
C. 124 Go Faster Green - 1 ball for all sizes

On Boy
A. 104 Boogie Board - 4 (4, 4, 5, 5) balls
B. 112 Leapfrog Green - 1 ball for all sizes
C. 125 Base Camp Brown - 1 ball for all sizes