* Child's personality: Some children are more verbally expressive than others. A chatty child will say it much more frequently.
* Attachment style: A child with a strong attachment to their mother might say it more often as a way of seeking reassurance or connection.
* Mother's presence: The frequency will likely increase when the mother is around.
* The situation: A child might say "mommy" more often when they need something, are scared, or are excited.
* Age: Younger preschoolers (3-year-olds) might say it more frequently than older preschoolers (4- or 5-year-olds) as their language skills and independence develop.
* Other caregivers: If other caregivers are present, the frequency of saying "mommy" might decrease as the child seeks them out as well.
In short, it's impossible to give a quantifiable number. It's a normal part of language development and attachment for preschoolers to frequently use their mother's name, but the frequency varies greatly from child to child.