Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Seek emergency care for prolonged or repeated seizures, severe difficulty waking, sudden major weakness, breathing problems, or rapidly worsening alertness.
Do not wait for the next routine appointment.
Follow-up continues after active treatment.
Visits generally include symptom review, neurologic examination, and MRI scans scheduled according to the tumor and treatment history.
Scans may become less frequent if the condition remains stable.
The article also says
Monitoring may also cover growth, puberty, hormone levels, vision, hearing, learning, emotional health, and physical function.
School assessments or neuropsychological testing can identify changes in memory, language, attention, or processing speed so support can begin early.
Families should receive a treatment summary and survivorship care plan when available.
These documents record the diagnosis, surgery, medicines, radiation exposure, and recommended long-term monitoring, and can support the eventual transition to adult care.
Between visits, contact the care team about new or worsening headaches, repeated vomiting, seizures, weakness, balance changes, unusual sleepiness, vision changes, or loss of skills.
Every sign above is quoted from the sofidex article on Brain tumor - children. If you are not sure, err upward — it is always reasonable to be checked.