To find the percentage of the large buttons, we can use the formula:
\[ \text{Percentage} = \left(\frac{\text{Number of large buttons}}{\text{Total number of buttons}}\right) \times 100 \]
In this case, Kinsley has 3 large buttons out of a total of 50 buttons. Plugging in the numbers:
\[ \text{Percentage} = \left(\frac{3}{50}\right) \times 100 \]
Calculating the fraction:
\[ \frac{3}{50} = 0.06 \]
Now multiplying by 100 to get the percentage:
\[ 0.06 \times 100 = 6 \]
Thus, the percentage of buttons that were large is:
\[ \boxed{6%} \]