Have been a first-aid instructor with a voluntary organisation for years in the past, I would guess that the vast majority of such instructors (both voluntary & professional) would have very little practical experience in dealing with paediatric first aid, and would be simply passing on what they have learnt in books.
If at all possible, I'd look for an instructor with practical experience, e.g. paediatric nurse or doctor. And btw, not every nurse or doctor is expert in first aid - it is a seperate skill.