This was a simple puzzle, and I got correct solutions from Praneeth, Prartik Poddar and Suman Saraf. Well done all. I am borrowing the answer from Suman.

For this, the most likely answer is 3 blue eyed out of 4 children. (Important to note that there are other solutions too)

b -> blue eyed
t -> total
b/t*(b-1)/(t-1) = 1/2

the sanest solution without involving the wrath of family planning authorities is 3/4 🙂

[Next possibility would be 21 children of which 15 are blue eyed!]

Hope you all enjoyed the puzzle!