is there a site where you can submit a photos of parents and get a
generated estimation of what the child/ren will look like?

do a google search using the terms "photo" and "morph"

One site where you can download a trial version of some software that
will do what you want is:
http://www.stoik.com/products/morphman/mm1_main.htm look for the
MorphMan 2000 product.

The resultant picture will obviously depend on the pictures that you
feed into it, so if you want baby pictures of your future potential
offspring, input a baby photo of you and your partner.

(not sure how scientific all this is!)

Perhaps you should think about the feasability of such a product. 
Look at large families with 10 siblings.  How different do they all
look?  I can tell you such software would not have had a chance at
guessing my aunts and uncles.