The Shadow Kitten

There's a funny little kitten that tries to look like me,
But though I'm round and fluffy, he's as flat as flat can be;
And when I try to mew to him he never makes a sound,
And when I jump into the air he never leaves the ground.
He has a way of growing, I don't understand at all.
Sometimes he's very little and sometimes he's very tall.
And once when in the garden when the sun came up at dawn
He grew so big I think he stretched half-way across the lawn.