Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Call emergency services if your child is difficult to wake, has a seizure that does not stop, has trouble breathing, or becomes unresponsive.
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has chest pain, tightness or pressure lasting more than a few minutes
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
Someone who you believe has taken an overdose or swallowed something poisonous
2
Is any of this happening?
Be seen today
Seek same-day medical advice if the fontanelle is newly tense or bulging while your baby is calm and upright.
Crying, vomiting, or lying down may briefly make it look fuller, but it should settle afterward.
Get urgent medical help if a bulging fontanelle occurs with:
Fever, repeated vomiting, or marked irritability
Unusual sleepiness or difficulty waking
A seizure, weakness, or abnormal movements
Rapidly increasing head size
Poor feeding with a clear change from usual behaviour
3
Does any of this apply?
Book an appointment
Arrange a routine appointment if the fontanelle seems unusually large, is getting wider, or remains open beyond the age expected for your child.
Mention any concerns about slow growth, feeding, constipation, delayed movement or speech, unusual head shape, or bowed limbs.
Every sign above is quoted from the sofidex article on Fontanelles - enlarged. If you are not sure, err upward — it is always reasonable to be checked.