Depending on the needle size and the thickness of the yarn, this will fit from a newborn to a toddler.
You can make it bigger by casting on more stitches and knitting it longer.
I used a DK yarn and
size 3.75 and 4 mm needles.
Cast on 84 sts with the smaller needles.
Knit 2 Purl 2 rib for 4 rows (more if you want).
Change to larger needles and stocking stitch and knit in your own stripe pattern for 42 rows.
Cast off, fold in two and sew seams. (Or you can knit halfway along the row and do a three-needles cast off for the top seam.)
Make a pompom and sew on to each corner.