What is big and yellow and comes in the morning, to brighten mom's day?

“Sunshine”

While sunshine is big, yellow, and brightens the day, it doesn't specifically come in the morning to brighten 'mom's day' like a school bus does.

“Banana”

A banana is yellow, but it isn't big in comparison to a school bus and doesn't have a direct connection to brightening 'mom's day' in the context of a morning routine.

“Gold”

Gold is often associated with the color yellow and can be considered valuable, but it doesn't fit the context of something that comes in the morning to brighten someone's day.