World Showcase is a litmus test to see what kind of Disney guest you are. There are those who believe that if you are not riding a big attraction, or waiting to ride a big attraction, then you are wasting your time. There are others who can easily while away an hour in the museum in Japan, and another hour and a half in the department store there. If your family falls into the former category, you can zip through WS from 11:00 and be done by 3:00, and that assumes that you have a leisurely table service lunch. If you fall into the latter category, you will need more than a full day for WS. As noted above, you should consider splitting your Epcot days so that there is some Future World and some World Showcase in each day rather than doing all of one on one day and all of the other on the second day. I find that this breaks up the monotony and allows you to truly immerse yourself in the hands-on stuff in Future World instead of bouncing from one attraction to the next. Same with World Showcase. It is more fun to completely absorb a country before moving on without feeling the need to "pick up the pace" in order to complete the circuit all in one day.
And a world about "shopping". The stores in World Showcase are not really souvenir shops as much as they are department store type shops. Yes, the requisite gifts, t-shirts and coffee mugs will be available everywhere. But if one goes into, say, the store in Morocco looking for a Disney souvenir, they might turn around and walk out in about 30 seconds. But if you take the time to look at the different spices, and food products, and woven items, and brass items, you might look at your watch and realize that you spent an hour in there. For some, this is a great way to spend an afternoon. Others think it is crazy to devote time to doing this. This is why you will see all sorts of opinions about Epcot in general and World Showcase in particular. No one can predict what another person will like. I could give you my "Top 10 things to do and see in WS" and you might do all of them and conclude that I am insane. Or you might thank me for turning you on to stuff you never would have thought to do, or seek out. No way to know. Just give it a try with an open mind and see where you end up.