Thanks for putting your query up at HealthCareMagic. Probably your little son has a respiratory tract infection. Generally these are caused due to a viral infection and have an allergic component as well. Fever may also occur. The petechiae on the cheeks may be due to rupture of small blood vessels just below the skin due to forceful coughing. There is no need to be concerned at the moment. But the condition might require serious attention in case the petechial spots expand or recur elsewhere. I hope that this has not occurred just after the dose of DTaP. Do not worry because only two doses have been delivered. Just give the next dose as per schedule. Giving him some antiallergic and steam inhalation is likely to give him some relief. I hope that helps. Feel free to revert back in case of further queries if any.