Materials used.
Red Heart Baby Hugs. I think this yarn has been discontinued, but any size 3 yarn should work, or Caron Simply Soft size 4 seems to work up the same.
Size F (3.75mm) crochet hook.

Stitches used in US terms
Ch/ch chain
Dc/dc double crochet
Sl st/sl st Slip stitch
Beginning corner stitch (ch 3 dc, ch 3, 2 dc)
Corner stitch (2 dc, ch 3, 2 dc)

Stitches used in UK terms
Ch/ch chain
Tr/tr treble crochet
Ss Slip stitch
Beginning corner stitch (ch 3 tr, ch 3, 2 tr)
Corner stitch (2 tr, ch 3, 2 tr)