Is a toddler enrolled in full time preschool considered a full time student?

"Full-time student" generally applies only to students in college or higher. For a toddler it wouldn't make any difference, as far as taxes are concerned, whether the child is a full-time student or not. What particular tax provision are you looking at, or where are you being asked whether the child is a full-time student?

Why are you asking?  Did Turbo Tax ask you?  Better check the date of birth under My Info.

Q.  Is a toddler enrolled in full time preschool considered a full time student?

A. Simple answer: no.

But it's irrelevant. Full time student status allows a child over age 18 (but under 24) to continue to be a "Qualifying Child" dependent.