The first time your toddler bites another child at playgroup, the mortification is instant. But biting, hitting, and pushing are among the most common behaviours between one and three years old, and almost always developmental rather than aggressive.
Why it happens
Toddlers experience strong emotions but don't have the language or impulse control to express them acceptably. The prefrontal cortex, which handles impulse control, is barely functional at this age. When they want a toy and another child has it, the fastest available response is physical.
What works
Remove your child calmly. Get to their level. "No biting. Biting hurts." Then turn your attention to the hurt child - this also models empathy. Keep it brief. A dysregulated toddler can't process verbal reasoning.
What doesn't work
Biting or hitting back. A child under three can't make the logical connection between being bitten and understanding that biting hurts others - but they absolutely learn that adults use physical force.
Prevention
Watch for triggers - hunger, tiredness, overstimulation. Name emotions before they escalate. Ensure they get attention when behaving well, not just when they misbehave. Most children stop between three and four as language develops.