The neck x-ray shows

Prevertebral soft tissue swelling, raising suspicion for a retropharyngeal inflammatory process (cellulitis/abscess). There is straightening of the cervical spine likely from spasm of the neck muscles. Relevant negatives are no air/air-fluid levels and no evidence of a foreign body in the prevertebral space.

The patient underwent a CT scan of the neck subsequently which confirmed a retropharyngeal abscess.

On a paediatric lateral neck x-ray, if prevertebral soft tissue measures more than 7 mm at C2 and more than 14 mm at C6, it is considered abnormal. False widening of the space can be seen if the x-ray is taken with neck in flexion & if the x-ray is obtained in a crying child in expiratory phase.

The above patient was managed conservatively with intravenous antibiotics.

Further reading https://emedicine.medscape.com/article/764421-workup#c6