I've never been at that time so I can't say whether things will be any busier or not
I can't imagine for one second though that Disney would do anything that would exclude children, they are always central to everything that Disney does
In Epcot you can book the Valentine's Day meal, but it is very expensive, the rest of WDW does not do anything, excet a few special toys.
As Valentine's Day is on a wednesday the park with not be busy, its when it falls on a weekend that it is.