In this review, we summarized drug administration strategies for childhood diseases, such as childhood epilepsy and attention-deficit hyperactivity disorder (ADHD). Therapeutic drug monitoring is recommended for most antiepileptic drugs; however, dosage of these in the clinical setting is usually based solely on body weight or age. Other factors to be considered are dosage form and taste; these are particularly important in infants and toddlers as they affect the adherence to a given medicine and may impose a limitation on drug administration. In addition, we should be cautious about such side-effects as the effect on appetite. Special attention should be paid if there is a history of long-time treatment during childhood, because appetite loss or stimulation might have had a substantial negative impact on growth during childhood. We also briefly summarized newly introduced drug therapies for spinal muscular atrophy. These include gene therapy and exon-skipping drugs, which increase the amount of functioning SMN2 protein in skeletal muscles. In particular, the focus of this treatment is on the age of the patient and copy number of the SMN2 gene, both of which are key parameters.