The group contains:
Men = 3
Women = 2
Children = 4
Total people = 3 + 2 + 4 = 9
The total number of ways to choose 4 people from 9:
C(9,4)=4!×5!9!
=4×3×2×19×8×7×6
=243024
=126
For exactly 2 children, the other 2 must be non-children (men or women).
Non-children = 3 + 2 = 5 people
Choosing 2 children from 4:
C(4,2)=2×14×3=6
Choosing 2 non-children from 5:
C(5,2)=2×15×4=10
Total favorable outcomes = 6×10=60
The probability is:
P=12660
=2110
Therefore, the probability that exactly 2 of them are children is 2110.