The suggestion of the boy's attitude towards his parents based on the given lines is one of mischief.
This refers to the way and manner a person acts towards other people which is an off-shoot of their character.
Hence, we can see that based on the given lines, the boy is pleased that the sleep of his parents has been disturbed by barking dogs and he smiles scornfully which shows that his attitude is one of mischief.
This shows that the mentioned boy is a mischievous person as he is happy that the sleep of his parents is disturbed and this leads him to smile scornfully as this shows his mischief.
Therefore, the suggestion of the boy's attitude towards his parents based on the given lines is one of mischief.
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