Children will receive either salbutamol or formoterol by MDI. Participants will be explained about the study, spirometry and inhalation of medicine with MDI and spacer. Children will receive two puffs (100 microgram each of salbutamol) or Formoterol 2 puffs (6µg /puff) by MDI and spacer. Each child will be explained about the inhalation technique by using a MDI of placebo. After shaking the MDI it will be attached to spacer (700ml volume) and actuated. Child will be asked to take 5 tidal breaths. Another puff will be given by similar method.