Tea apparently isn't great as it can inhibit iron absorption. However if it is an occasional thing then it's just klike most other foods/drinks that aren't great for you - it should be a sometimes food.

DD1 has asked for tea with us since she was about 18m so we have let her have it on weekends. We basically fill her cup with milk and add a small amount of tea to it and she is happy with that. I know it isn't great for her but I think once a week in lots of milk is fine.