The charities have a lot of information on their websites, below is some general advice to help you get those needles clicking.
Bliss: One of the many ways that you can support Bliss is by knitting for babies in special care units. Knitted items are most helpful for babies about to go home, but there is also a need for blankets and hats for babies in hospital. Knitted items are often not suitable for intensive care units – stitched cotton is preferable. However for larger babies, and in high dependency and special care units, knitted items are often very welcome.
At AllAboutYou you will find free patterns from Debbie Bliss and Erika Knight, both noted children’s knitting and crochet designers, who create beautiful traditional patterns, with timeless style that can be passed down for generations. You will have such a hard time making a decision just which knitting or crochet pattern to tackle first… So many hats, sweaters, cardigans, vests, and blankets.
Bonnie Babies mainly makes blankets for premature babies. They provide patterns for toys, hats, and sweaters (including a ”5 Hour Baby Sweater!”), but blankets are quick, simple to make, and guaranteed to fit. Families can then continue to treasure them long after the child is grown.
Early Angels: This is a site based in the U.K set up to help people to knit, crochet or sew clothes, blankets and other keepsakes for premature, low birth weight and sadly stillborn babies. They have a wide range of free knitting, crochet and sewing patterns accessible on their pattern page.