A boy settles into the hay for a nap, an owl flaps out, and off he runs. It is a small, funny fright rather than a real scare, and toddlers tend to enjoy the sudden dash at the end.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
A little boy went into a barn,
And lay down on some hay.
An owl came out, and flew about,
And the little boy ran away.
Public domain. Text from The Real Mother Goose (Blanche Fisher Wright, 1916), via Project Gutenberg. View the source edition