As someone who was also in two minds about midwifery and child nursing, I suppose it really comes down to this:
1) Do you want to support a mother (and often their partner) through pregnancy, antenatal care, labour, delivery and then support the mother and child for roughly a month afterward (depending on condition of baby) - Midwifery actually has less of a focus on the baby, but more on the baby while it develops in the womb, with a focus on the mother and her wellbeing.
2) Do you want to care for children facing a variety of illnesses? Does the idea of supporting a family and their child with adjusting to long term conditions, short term problems or promoting health in children appeal to you? Child nursing is much more focused on the child, ranging from 0-16 (sometimes up to 18 depending on the ward/community team), however supporting the family is also crucial.
As it has been said, both fields are notorious to get into, but as long as you demonstrate an understanding of the role, what has prepared you and apply your experience (which is crucial), and meet entry requirements you have a good shot. If you have any questions about either field, I can answer about child and chat with my midwifery flatmate to help answer any midwifery questions you may have. I wish you the best in choosing your field, I know it isn't easy - there is always the option of doing adult first (you still have to be committed to this field of nursing and gain experience), as child and midwifery are both possibilities with this qualification.