Respiratory diseases, such as asthma and bronchitis, and ear infections are the most common diseases among children. Study that researched the effects of the secondhand smoke on infants during their first year of life found an  association between maternal smoke and incidents of respiratory diseases among infants (Pedreira et.al., 1985). You can prevent your child from suffer recurrent illnesess by protecting him from secondhand smoke.

Reference: Pedreira et.al. (1985). Involuntary smoking and incidence of respiratory illness during the first year of life.