"with a sexual interest in children" is a new nebulous and undefined term which has surfaced over the past few years.

In a number of cases where it has been used, it has obscured rather than illuminated. It originates from a few forensic psychologists, and it has been used to profile criminals within groups of criminals. On occasion, it might be lazily invoked without really reckoning with how it is not for the general population.

Consequently, when it is used, it might be used as a slur or to dehumanize individuals by alluding to a criminal connection.

The "with" originates from person first language, a purportedly destigmatizing linguistic style where someone might be referred to as, say, "someone with a criminal history" rather than a "criminal". Here it is used primarily to perpetuate stigma thereby mooting it's purpose.

The way it is worded is also prone to misuse and tends to distract rather than add value to discourse. What is "interest"?

I strongly recommend against using it.