I work as an adult HCA and guess you will be asked some of the things I was asked in my interview, like why do you want to be a HCA?
How do you feel about dealing with wee, poo, blood, vomit etc.?
How would you cope if you had a bad shift e.g. saw something upsetting? (I said if I was really upset I'd go talk it over with the hospital chaplain (who happens to be a family friend), they seemed to like that).
What does being a HCA involve? Seriously, you'd be surprised how many people apply for HCA jobs having no idea. Answer: feeding, dressing, toileting (including changing incontinence pads (lots of people are incontinent when they're seriously ill), emptying catheter and colostomy bags and putting people on bedpans), bathing, observing vital signs (blood pressure, pulse, respiration rate, temperature, oxygen levels, blood sugar), filling in nursing documentation, cleaning, making beds, repositioning people in bed (can involve rolling, (gently) dragging and hoisting - it's hard physical work, with bedbound adults anyway). You may also be trained to take blood or insert cannulas.
How would you maintain patient confidentiality?
A big part of paediatric nursing is supporting/reassuring the family so I bet you'll be asked about that.