A pea-sized amount of fluoride toothpaste is sufficient. Fluoride toothpaste helps to prevent tooth decay but excessive use can cause flurosis (yellow-brownish spots that appears on tooth surface)
Visiting the dentist early and regularly is a part of good oral hygiene practice. Bad habits like thumb sucking and eating sweets just before bedtime should be discouraged as they promote bacteria growth which might lead to tooth decay.
If decayed teeth is detected early, fillings or even "root canal treatment" for children can be done to save the teeth. This lowers the possibility of extracting premature tooth that might lead to future crowding of permanent teeth.
Thus, it is recommended that your child visits the dentist early and regularly from around the age of 1. Early dental check-ups will also help prevent dental phobia.