Hi there! I also did Access to Higher Education in my late 20's (a bit later than you!) and am now in the first year of a Midwifery degree. Obviously, I can't tell you whether to go for Child Nursing or Midwifery but what I would suggest is that you make your decision before you send your application through UCAS. Both Child Nursing and Midwifery courses are heavily over-subscribed and any applications which do not show full commitment to a specific path are more likely to be rejected.
It's definitely worth looking into each career in more detail, and thinking about the type of clientele you'd prefer to deal with; as a child nurse, you will be dealing mainly with poorly children and their families. The work can be extremely challenging, but very rewarding, and you obviously have to have a huge amount of patience and a natural love of children.
As a midwife you will be mainly supporting well women and their families through a normal life experience, generally with a positive outcome. If it's babies you particularly want to be dealing with, then midwifery probably won't be for you as the actual contact with the baby is a very minimal part of the job.
Have a look at the NHS website for more information about both careers and the options available long-term for career progression and areas in which you can specialise. Also bear in mind, though, that whichever course you opt for, you certainly won't be 'over the hill' once you qualify and will still have plenty of time to do further training later on if you wish. One of my fellow students has just started her Midwifery degree at the age of 50!
Good luck whatever you decide, and I hope you enjoy your training and subsequent career. All the best!