Toddlers do need helmets for tricycles.
If the toddler is riding a tricycle on pavement then they should really wear a helmet as it's possible for the toddler to fall over and hit their head or get injured some other way.
However on the grass in the yard then there's no need for a helmet as the grass and dirt is soft enough to not cause any severe injuries.
But if the toddler is riding the tricycle on the sidewalk or on pavement elsewhere such as the park then have them wear a helmet for safety.
This also gets the toddler into the habit of wearing a helmet which they should do when riding a bicycle when they get old enough.
From around 1 to 2 years old, a toddler will have developed the gross motor skills needed to start learning to pedal a trike although of course all children develop at their own pace.
A trike offers an early opportunity to learn how to pedal.
Although babies under 1 year should not wear helmets because they have a weak neck structure.
Babies younger than 1 year old have weak neck structures and shouldn't wear a helmet or travel on a bike.
After a year old, toddlers can begin to ride tricycles and ride in seats or carts attached to an adult's bicycle.
Generally a kid can pedal a tricycle properly when he or she is around 3 years old.
The tricycle size should be according to the kid's height.
Children should always wear a helmet while riding a tricycle.
Make sure the height of the tricycle is comfortable.