Mel, the dose for a 6kg child would be 2-4ml a day.

So 2 would be the lower end, divide that by the number of times a day you give it and that is the dose.

For the higher end, 4 ml would be the daily dose, divide that by the number of times a day you give it and that would be the dose.

Dosing for zantac is
weight (in kg) x 5 (for minimum or 10 for maximum) divide by 15.

It may take a week or so to notice true difference, but I think that you should get it upped to those doses for the best effect. I used to increase Parkers every 100g gained, it was that sensitive for him,.