I often check out our opposition sites (the beauty of Google) and see what they are selling and whether I'm competitive, have a good range to choose from, etc.
One of the things I notice time and again are baby bracelets advertised which are 6 inches long. Now 6 inches is far too long for a baby bracelet. It would go round the wrist of a newborn twice. If you're looking for an item of baby jewellery for a newborn, take notice of sizes. You don't want it put away for years in a cupboard until it fits. A bracelet 6 inches long would fit a child over age 5, and very often up to the teens. Of course, baby and children's wrist sizes vary a lot but this is a general rule.
A baby necklace should be 12 inches or 13 inches, not 16 or 18 inches. It will reach her navel! For toddlers, a 13 inch is perfect, 14 inches for a larger child or perhaps a child around age 5. Older children's necklaces are generally 16" and adult's necklaces are usually 18".
Baby bangles and bracelets should be adjustable in size, ideally. Bangles that expand and bracelets that either have an extension, or there are two clasping points along the length of the bracelet so that your baby/little girl can wear her jewellery for many years.
If you don't know what size to purchase and can't measure the child's wrist, and she has her ears pierced, baby and children's earrings are a much safer bet. Earlobes of babies don't grow much at all so any earrings will fit. But most people like baby earrings to be very petite. But the beauty of this is, she can wear those baby earrings all her life! The length of the rod is more important, so always buy children's earrings, not adult. Children's earrings will fit an adult but adult earrings will have a rod that's a little too long.