To find the ratio of children to keychains, we need to determine the total number of keychains.
Since there are 6 children and each child has 2 keychains, the total number of keychains is: \[ 6 \text{ children} \times 2 \text{ keychains/child} = 12 \text{ keychains} \]
Now, we can write the ratio of children to keychains: \[ \text{Ratio of children to keychains} = 6 \text{ (children)} : 12 \text{ (keychains)} \]
This simplifies to: \[ \text{Ratio} = 6:12 \]
So, the correct response is: 6:12 (ratio of 6 to 12).