Look what it says on your toothpaste tube:

Colgate:
“To prevent swallowing, provide adult supervision and use only a pea-sized
amount for children under six years.”

Crest:
“Do not swallow. Children under 6 years of age should use only a pea-sized
amount and be supervised while brushing.”

And how much added fluoride in municipal or bottled water is your child
drinking every day?