Based on your description of the scatterplot titled "Hours Playing with Toys," the most plausible conclusion about which age group spends the most amount of time playing with toys would depend on the visual representation of the data points plotted.
Typically, younger children, particularly those in the 2- to 4-year-old category, tend to spend more time playing with toys compared to older age groups. Therefore, if the trend follows common expectations, the most plausible conclusion would likely be:
The age group that spends the most amount of time playing with toys is 2- to 4-year-olds.
However, without seeing the actual scatterplot, it's difficult to make a definitive conclusion. If the scatterplot clearly shows a different age group having the highest hours, that would change the answer.