Children can safely use some allergy medications, as long as they are given in an age-appropriate dosage. However some side effects – such as drowsiness or hyperactivity – can be more exaggerated in children.
Never give medication to a child before consulting a physician. Drugs and their potential effects on children include:

• Antihistamines. Many antihistamines cause drowsiness in adults, and this effect can become even more pronounced in children. Conversely, other children become extremely jittery after taking antihistamines. Other symptoms that may appear in some children (especially under age 6) include insomnia, nervousness, euphoria, tremors and seizures.
  
  
• Decongestants. These drugs are related to adrenaline, and can make some people jittery. Children are particularly susceptible to this effect, and should take only decongestants formulated for their age group.
  
  
• Corticosteroids. Some injected and oral corticosteroids may impact growth in children and affect the adrenal gland (kidney portion that secretes natural steroids). Children (aged 6 to 12) usually are prescribed corticosteroids in nasal form or inhaler form only, with dosage amounts adjusted for their age and size. Corticosteroids may be less effective in treating infants under the age of 1 year.
  Cromolyn sodium. Because of its relative absence of side effects, cromolyn sodium can be safely used by children as young as 2.
  
  
• Bronchodilators. These are generally used on an as-needed basis when a child is coughing, wheezing or short of breath. Studies performed to date have not demonstrated specific problems that would limit the usefulness of bronchodilators in children.