Plain Toothpaste contains 1000 ppm fluoride — the standard adult concentration. Under current Australian guidance (NHMRC; Australian Dental Association, Guidelines for use of fluorides in Australia: update 2019), this strength is appropriate for children aged six and over, brushing twice daily with a pea-sized amount and spitting rather than swallowing.
For children aged 18 months to 5 years 11 months, the same guidance recommends a low-fluoride children’s toothpaste (around 500 ppm) — Plain Regular is not formulated for that age group. Under 18 months, no toothpaste is recommended; brush with a soft brush and water only.
For children at high caries risk, your dentist may recommend a different regimen at their discretion. Follow their advice, not ours.