It's very normal. I've heard it happening quite a bit (though to be honest usually when the baby is younger than Caleb). She's at an age when she's likely to take interest in something she sees everyday. She's a mini-scientist.
How you react is very much up to your comfort levels. But I think you have to extend Tracy's philosophy here - the bit about 'start as you mean to go on'. So if this doesn't feel great and you are praying it only lasts a couple of weeks then I would rethink. Just gently mention that Caleb needs his milk and she's a big girl and gets to eat things he can't. Perhaps she could have some in a cup instead when he's done. Or she could have a special kind of hug if she's seeking physical contact.
However if you are prepared for this to last perhaps months and months (and it may well last that long if she is in control and she becomes more established) then don't do anything.
