Wow, it;s been a long time since I've been on here. I hate being so busy

Well, I have 2 questions for all of you:
1) I need to know how I count up children as part of the total guests needing food for the weding. I know that 2 children under 10 count as 1 adult but at what age would you add kids as part of the kids under 10. Let me rephrase...obviously a 2 month old baby doesn't need to be counted at all but at what age would I add a child as part of that "2 for 1"?
2) I need to give the seating chart to my venue pretty soon. Do I provide a chair for every guest including babies? I know babies won't sit on their own but I figured if they had a carrier it would be nice to put them in a chair next to their mothers (no additional cost for extra chairs). Or do the baby carriers typically go on the floor?
Any feedback is greatly appreciated!