U can try Q & M and city square mall...
They have PD Dentist and also GP dentist which can handle toddlers.
They have rooms for children. Consulation is $50 each visit.
fusionpolis has 1 dentist very good .. they have 2 branches. 1 at holland village, 1 at fusion polis. i bring my 3 yr old son there for half yrly check up and they do not have very long queue coz they go by appointment only.