Hi Maryam You should encourage your child to brush his teeth in any way you can. My son had a similar problem when he was 3 and I kept trying many brands until he tolerated a brand called Pierrot. So you should try different brands and flavors until something suits him. Another tool to help is gargling in cold water as it gives a numbness effect to the mouth. Also distracting him while brushing by shaking his other hand or dancing or breathing through his nose might help too. Until you find the suitable toothpaste, brushing with water only is recommended. Gag reflex usually decreases as the child gets older but brushing is mandatory at all stages. A visit to the dentist to emphasize importance of brushing to child and parents is indicated too. A reminder: Teeth brushing should start as soon as the first tooth erupts but without toothpaste ( or with fluoride free toothpaste for children under 2/ not available much in Jordan) and with fluoridated kids toothpaste for children above 2 twice daily and for 2 minutes. Good luck!