If your 4-year-old daughter has an ulcer in her mouth, you can first try monitoring it for a week to see if it improves on its own. If it persists, you could try applying Orabase™ to help with pain relief and healing. In the meantime, you can give her some Tylenol™ for pain and encourage her to eat soft, non-irritating foods. If this is a recurring issue, it may be a good idea to consult a dentist to investigate further.