That's wonderful - I know you will have a fantastic time, and with those little ones being right on top of the park entrance will really feel like luxury.
As for taking drinks, I would have to say that's one of my little complaints about Castle Club. The answer is no, nothing is supposed to be removed from the lounge. At WDW the concierge service includes being able to take soft drinks and bottled water out of the lounge, and snacks, etc. to the rooms. Castle Club does not provide this, even though their rates are actually quite a bit higher. Since it was winter this was not such a big concern for me, but in the summer it would be nice to have water provided. It is nice, however, that you can nip back into the hotel whenever you want for a sit-down in the lounge and some hot chocolate, coffee, or something stronger - Yes, there is a full bar in the Castle Club lounge. Also, something that Castle club has that the WDW concierge lounges do not, is full service. You can sit down and be waited on "hand and foot". Breakfast and tea are buffets, but drinks are served by the very courteous and solicitous CMs, as they are throughout the day. And even at breakfast and tea, the CMs are constantly coming to your table to ask if there is anything you need. Especially when you have kids, it's nice not to have to bounce back and forth time and again between your table and the buffet for the things you "forgot" or your kids decide they want during the meal. The CMs will gladly do that for you. Drinks are served in glasses, at table, not simply picked up in bottles or cans - it's just a cut above the WDW concierge service in it's attention to classy detail. Try to get the table to the far left and all the way inside - at the full window - it has a glorious view right down Main Street to the Castle!!
Any other questions that come to you - keep them coming. I'm excited for you and your family.