The chest x-rays shown are inspiratory and expiratory views.
The inspiratory chest x-ray does not show any concerning features (I.e. foreign body, pneumothorax, or air space consolidation).
The expiratory chest x-ray is abnormal; there is significant hyper-expansion of the right lung field.
This toddler has inhaled a piece of a plastic toy. Based on the chest x-ray features, this is likely to have lodged in the right main bronchus.
Radiolucent foreign bodies such as plastic and food particles are not appreciated on a chest x-ray. An indirect sign associated with this presentation is a hyper-inflated lung field on the affected side, due to the ball valve mechanism. The hyper-inflation becomes particularly apparent in an expiratory film.
If the child is too young to understand instructions, a decubitus chest x-ray can be taken with both sides dependent. The side of the lung which does not collapse (i.e. remains hyper-expanded) is the affected side.
A low dose CT chest or direct visualisation with bronchoscopy are the definitive ways of confirming a bronchial foreign body in children.