I've had this pattern for many years, just jotted on a scrap of paper, and have occasionally adapted it slightly, but to be honest, it's technically not mine. So I hope that by giving the pattern here I won't be contravening any copyright law!
Using 4ply wool in lemon or yellow and using No 3(11) needles, cast on 26 stitches.
Row 1 - K
Row 2 - Inc, K10, inc, K2, inc, K10, inc
Row 3 and alt rows - K
Row 4 - Inc, K12, inc, K2, inc, K12, inc
Row 6 - Inc, K14, inc, K2, inc, K14, inc
Rows 7-14 - K
Row 15 - Inc, K to end, Inc
Row 16 - K
Row 17 - As row 15
Row 18 - K
Row 19 - As row 15 (44 sts)
Row 20 - Cast off 12, K20, cast off 12
Rejoin wool to remaining 20 sts
K 14 rows
Pull wool through remaining stitches and gather tightly.
Sew seam, stuff head with cotton wool or toy stuffing fibre, run a thread around the base of the neck and pull tight to shape and finish off loose ends.
Embroider eyes with black thread, or use felt dots
Cut beaks from orange felt and sew on, or knit from contrasting orange or dark yellow wool.
The beaks on mine are literally three stitches cast on and cast off again, but you can do anything you like.
You can use "fluffy" wools to give a different effect, especially some of the baby wools that have a fleecy feel. I've knitted the chicks in double knit and chunky wools too (you might want to adjust the pattern or your needles a bit if using chunky as they come up much bigger).
I've also knitted hens using beige or brown, and create a little comb from red wool.
These I knitted in stocking stitch instead of plain knitting but they don't look quite right somehow.