Let's denote the regular price of the movie ticket that Michael paid as \( x \).
Since it cost $2 less for his brother, the child price would be \( x - 2 \).
According to the problem, the total cost for both tickets is $12:
\[ x + (x - 2) = 12 \]
Simplifying this equation:
\[ 2x - 2 = 12 \]
Now, add 2 to both sides of the equation:
\[ 2x = 14 \]
Now, divide both sides by 2:
\[ x = 7 \]
So, the regular price (Michael's ticket) is $7. Therefore, the child price (his brother's ticket) is:
\[ x - 2 = 7 - 2 = 5 \]
Thus, it cost Michael's brother $5.
The answer is $5.