Birth onwards (based on weight)
(1.5 x weight in kg) + 10 = Percentage of adult dose

2-12 years of age
(weight in kg X adult dose)/67 = childs dose

(Age of childs next birthday / 24) = percentage of the adult dose. 

For infants up to 2 years of age
(age in months x adult dose)/150 = childs dose

Up to 30 kg
(weight in kg X 2) = percentage of adult dose to give

Over 30 kg
(weight + 30)= percentage of adult dose

For infants up to 2 years
(age in years X adult dose)/(age + 12) = childs dose