Children’s teeth need particular protection as they develop. Suggestions include:
Brushing teeth without toothpaste until the age of 18 months
Introducing a low-fluoride toothpaste when a child is approximately 18 months old. Choose a low-fluoride toothpaste designed especially for children
Using a child-size toothbrush with soft bristles
Using only a pea-size amount of toothpaste, smeared over the toothbrush
Encouraging children to spit out toothpaste, not swallow it. Don’t rinse
Supervising children when they brush their teeth until you are sure they can do it well
Continuing to use low fluoride toothpaste for children until they are six years old
If your drinking water is not fluoridated, seek professional dental advice about the use of fluoride toothpaste for children. A dental professional may advise more frequent use of fluoride toothpaste, commencement of toothpaste at a younger age or earlier commencement of use of standard toothpaste
Taken from https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/dental-care-fluoride