Daughter is 4 years old, fell from a pub height chair and hit head on tile floor. Has a large knot on side. Playing as normal. Call her doctor or ER?

Watch. As long as she is acting ok and not showing signs of significant head injury such as vomiting, sleepiness ( at a time when she usually doesn't nap), or extreme fussines. This close observation should last 2-3 hrs as delayed symptoms in toddler head trauma are rare.