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My parents are visiting USA from India and are planning to bring me a few sweets and snacks that may contain egg, milk and/or cheese related products. The regulations on this seem a bit murky.

https://help.cbp.gov/app/answers/detail/a_id/82/~/travelers-bringing-food-into-the-u.s.-for-personal-use

The above link says

Bakery items, candy, chocolate, and dry mixes containing dairy and egg ingredients [such as baking mixes, cocoa mixes, drink mixes, instant cake mixes, instant pudding mixes, liquid drink mixes containing reconstituted dry milk or dry milk products (including those that contain sugar), potato flakes, and infant formula] commercially labeled and presented in final finished packaging are generally admissible.

And at the same time

Meat, milk, egg, poultry, and their products, including products made with these materials, such as dried soup mix or bouillon, are either prohibited or restricted from entering the United States, depending on the types of animal diseases which occur in the country of origin.

So is it okay or not okay to bring these since these are mostly 'bakery' items (I am talking about sweets similar to baklava). If they do bring it, are they supposed to declare it anywhere? They are transiting in Abu Dhabi and will have pre-clearance done there so does this change anything?

The first paragraph only refers to commercially packaged and labeled products. Elide the part between the square brackets to see that. At least here, I don't see Indian sweets with what I would call commercial labeling (ingredients list etc.). The packaging may be exceptionally fancy but they are otherwise similar to home-baked goods.

commercially labeled and presented in final finished packaging are generally admissible.

I would guess they might not be admissible, but that will depend on the customs agent. You must declare it honestly on the customs card, preclearance or not makes no difference, except where you leave the stuff if it's not admissible.

Don't even think about 'forgetting' to declare it. They don't have much of a sense of humor about such things.

Because you're transiting through an airport with US preclearance, Etihad recommends that you carry food items in your carry-on luggage. If the food is in your checked luggage, then it has to be brought up from the baggage area for inspection, then returned, which can add a significant delay to your customs clearance, and possibly cause you to miss your flight.

Always declare your food. Tick the appropriate "Yes" box on the landing card. If the food is not allowed, they'll just throw it out, but there is no other penalty. But if you don't declare it, you could get a very steep fine, even if the food is allowed! There are dogs trained to sniff food, so it's rather pointless to try to sneak anything in.

CBP has a guide on what food items are generally allowed. In general, baked goods are OK, but the rules are quite complex and can change quickly, so if you aren't bringing something obviously prohibited like meat, your best bet is to simply declare the food, explain what it is, and let the CBP officer make the determination.

More important than the dairy is the egg. Given the threat posed by bird flu they're very skittish about eggs. As Michael Hampton said, always declare, always tell the truth about what you're carrying. There's no penalty (beyond the loss of the item) if they decide no, there can be substantial fines for trying to slip something past them.

In general if the method of preparation of the product (what has already been done, what you will do in the future is irrelevant) will have destroyed any pathogen short of a prion they'll let it in but I've seen them categorically reject egg regardless of form. (That happened to someone in front of us and probably off our plane--which was coming from an area with an outbreak.)