I don't know about the lettuce, since my kids (age 8, 5,& 3) still won't touch it. But we keep trying...
As far as tea, I think it is fine to give it to your toddler as long as you are aware of what is in it. All black teas have a higher caffeine level and so I would avoid those, but rooibos teas - sometimes called red teas - have NO caffeine as well as NO tannic acid. That is what I give to my kids. Also some herb & fruit teas are good, but I would agree with others that you need to watch what is in them.
All true teas (black, green, white) have tannic acid in the leaves, but it is only released into the tea if you steep it too long. You'll know when you do because the tea will taste bitter. Just follow the steeping time on whatever tea you have and it will not be an issue. I have no problem giving these teas to my kids (as long as they are decaf).