Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Use emergency services for severe breathing difficulty, blue or gray color, prolonged pauses in breathing, or reduced responsiveness.
Seek urgent medical advice rather than waiting for a routine visit if breathing becomes harder, the child drinks much less, wet diapers decrease, or the child seems increasingly sleepy or unwell.
Follow-up needs depend on the child's age, health history, and symptom severity.
A clinician may recommend a recheck for a very young infant, a child with a higher-risk medical condition, or anyone whose feeding or breathing needs closer observation.
Arrange routine follow-up if the cough is not gradually improving, symptoms return after improvement, wheezing keeps recurring, or there are concerns about feeding, growth, or sleep.
A lingering cough by itself does not always mean that antibiotics or an X-ray are needed.
The article also says
During recovery, watch the child's breathing, fluid intake, wet diapers, alertness, and color.
Symptoms often worsen before they improve, commonly reaching their greatest intensity around days 3 to 5 of the illness.
Nasal congestion and feeding usually improve first.
The cough may last for several weeks.
Before returning to childcare, consider whether the child is fever-free, able to participate comfortably, and feeding well enough.
Childcare programs may have their own illness policies.
Every sign above is quoted from the sofidex article on Bronchiolitis. If you are not sure, err upward — it is always reasonable to be checked.