If you are not planning to buy a ticket for your 4 year old (which you can), you would be better off in 2A (though 2A is more expensive than CC, so it defeats the money reason). 2A is very comfortable with big seats (around 2.5 times a CC seat in width and much more leg room as well) and can easily accommodate your youngest on your seat. It will have less people and will be less noisy. In CC, if the train is full, you will have to put the child in your lap, unless you buy a ticket and those seats in CC are not very big. Also, 2A is more comfortable if you wanna lie down (especially for the kids), which you cannot in CC and has way more baggage space under the seats compared to CC.