Our 20-month son has started falling sick quite often every since he
started going to day care.  He was at home for the first year and he did
not fall sick even once.  Now it seems like he has some sort of cold or
flu pretty much once a month.  Most of the time the cold leads to an ear
infection as well, with the result that he ends up being on antibiotics
3 weeks out of 4.  I know kids in day care fall sick more often, but we
are beginning to wonder how often "more often" really is, whether our
son is more susceptible or has lower immunity than average, what the
longer-term effects of constantly being sick and taking antibiotics are,
and what we can do to build up his resistance.  He really enjoys his day
care and we think it's great too, but we are beginning to wonder whether
we should think about getting a nanny.

Are there any studies that can help answer some of these questions?

-- How often do kids in their first, second and third years fall sick?
How often do they get colds, flus, ear infections?  Is there any data on
home care vs. day care?

-- Does being sick "build immunity" (leading to less illness later),
does it make kids "weaker" (leading to more illness later), or does it
not have any long term effect?

-- Does taking antibiotics on a regular basis have any negative long
term effects?

-- How does one tell if a child is more susceptible to illness than
normal, and what does one do about it?

-- Is there any way to build immunity and resistance?

Any data, information or advice relating to this would be much
appreciated.  Thanks a lot.