@CountryQueen - I'm talking about the person at the front, where the baskets/trays are. Off the top of my head from recent flights - Geneva, CDG, Toronto, Ottawa, Montreal, Manila, Doha, San Francisco, Munich, Port Moresby, Nairobi, and Hobart. I don't remember for Sydney and now that I think about, I think they didn't in Hong Kong as you had scanned it just before and you were in a gated area between that scan and the security belts.
To be clear, they aren't looking so that they know how many baggies of liquid you can have, but they are checking at/with visibility of, where you are putting your things on the belt (not all airports make you remove liquids, and some don't make you remove anything).
Anyway, it doesn't matter as I agree that (a) many airports don't even worry about the baggie anymore; (b) I've not seen any what are being strict about liquids in the baggie even if you do have to remove them; and (c) the baby should get their own baggie. I was just answering the question of how they could possibly know if the baby were a lap child or not (though this clearly depends on the specific airport).