My 5 y/o repeatedly tells me that things look small. i will look the size of a mouse. is this micropsia? what are causes? no other symptoms.

Micropsia: There is something called "alice in wonderland" syndrome, where the person experiences transient distortions of body image or visual images. It's episodic, & can cause things to look very small (micropsia) or very big. It can be a migraine equivalent (no pain necessary), or a variant of epilepsy. There are even reports of lyme disease showing up that way. You may want to consult a neurologist.