Why is "mixing" used instead of "to mix" in "didn't want Dudley mixing with a child like that"?

Question

I started reading Harry Potter and there is a sentence:

They didn't want Dudley mixing with a child like that.

I understand the meaning of the sentence, but could someone explain why mixing is used, but not to mix ?

I expected a sentence like that They didn't want Dudley to mix with..

Answer 1

"Want to mix" and "want mixing" are two forms of a "double verb construction." (hku.hk) - The second verb can be in a "to-verb," in a "verb-ing" form or just in "verb" form.

Example:

• He helped to treat him
• He helped treating him
• He helped treat him

The forms can be interchangeable, but can have a subtle different meaning. The "to" form emphasizes a result of action and the "-ing" form an action in progress.

Answer 2

To want [someone] to do something

To want [someone] doing something

the ing form here would be a gerund referring to the activity.

• His mother did not want him swimming in the rough sea.
• My father wanted me studying at university not working for an Internet company.

The to form is more a purpose or end result wished for.

His brother wanted him to find a job. [end result]
His brother wanted him looking for a job. [engaging in the activity]