What is the harm with a toddler drinking coffee?

Aubrey

My 16 month old seems to have a taste for coffee and tries to drink mine. When she's with her grandma she drinks hers but coffee is sacred to me. Today she threw a big enough fit I gave her the last sip of mine. She doesn't get caffeine anywhere else if I can help it. I'm wondering if this will be a problem later. Am I going to have to send a thermos of coffee with her everyday when she goes to school?