Hi,
Our LO (23 months) is on Abidec (multivitamin drops), the dosage is on the packet. I know what you mean about Heath Visitors, advice can be conflicting.
The way I think of it is, its certainly not doing her any harm and she has a very healthy, balanced diet anyway, plus she likes to take them, so its a no-brainer really (I think if it were a battle, it would be a different story).
HTH