There are a number of ways of estimating children's DOSES from preclinical (adult) data - often depends on the therapeutic index of the drug in question (the WIDER the therapeutic window the less ACCURATE the child's dose needs to be). Sometimes straight weight-basis i.e. 7kg child gets 1/10 dose of 70kg adult.
More accurate (so they say) is a dose based on body SURFACE area (child's surface area is greater in PROPORTION to its body weight than an adult is). There are normograms to calculate surface area from weight and height of child.
All of these may be wrong if clearance of drug in child is significantly different from adult e.g. different metabolism or different route of clearance.

There are a number of ways of estimating children's doses from preclinical (adult) data - often depends on the therapeutic index of the drug in question (the wider the therapeutic window the less accurate the child's dose needs to be). Sometimes straight weight-basis i.e. 7kg child gets 1/10 dose of 70kg adult.
More accurate (so they say) is a dose based on body surface area (child's surface area is greater in proportion to its body weight than an adult is). There are normograms to calculate surface area from weight and height of child.
All of these may be wrong if clearance of drug in child is significantly different from adult e.g. different metabolism or different route of clearance.