不過,
to take photos of babies/children indoors,
we need a small number (wide) focal length.
e.g. 18-55mm
Otherwise, with a large number (tele) 55-200mm, maybe,
only the face, or part of the face, of the child can be seen.
And there may not be enough room to
step back to take the whole body (head, body, feet) photos.
The 55mm to 200mm that you mention
is better when you want to take a photo from far away, and you don't
want the "subject"/thing to look too small.
E.g. taking photos of a far away bird...
In other words "tele" magnify things more.
So, the 55-200mm complements, rather
than replace the 18-55mm.
There is also a 18-200mm available.
(for your information)
What is your reason for getting
the 55-200mm?
If it's want for a "better" or "more
prestigious" lens, then, the
f/2.8 large aperture lens are generally
considered more "professional"
Yet, a lot of professional zoom lens
are around HK$12,000 or more.
The 18-55mm Kit lens is not
the highest quality(e.g. the 14-24mm f/2.8)
but is generally considered quite good.
So, in my humble opinion, you can
consider to use the 18-55mm for a
while first.
If you find that you often take
photos of far away things, and that
the 55mm end is not "long"/"tele"
enough, then
Option (1) get the 55-200mm and keep the
18-55mm.
If you later find out that you have
no need to use 18-55mm, then sell it.
But, as this is baby-kingdom, I assume
that you would take photos of children,
and the 18-55mm should be a neccessity.