Hello You can use thyroxine for your children and dosage are adjusted according to weight of child and also according to age as follow. Age 1-5 years :5-6 mcg/kg/day; 6-12 years :4-5 mcg/kg/day. Age 12 years:2-3 mcg/kg /day. You mentioned that there is thyroid problem but didn t mention the name of disease so very difficult to say something . But thyroxine is used in Replacement therapy in Hypothyroidism. Severe and chronic hypothyroidism TSH suppression. The side effects are :Nervousness , excitability , tremors, muscle weakness, cramps, sweating , flushing, heat intolerance , headache , insomnia etc . Since this medicine is very important for your children , so continue it because side effects are very minor and rarely . I mentioned in detail but you can continue this medicine after the advice of your treating physician . Good luck.