I second the Rooibos, it is a lovely tea and I find it works well for us as it is good with milk as well as black so DD (2.5yrs) thinks she is being just like me when I make it for her! (Well she is being just like me when I drink it too!!)

When I'm in a rush and making a tea with a tea bag, I make a small weak version for DD by dipping my used tea bag in a bit of water in her cup for a brief sec just to colour the water. Then she adds milk and is very happy with herself.