It's easy to be wise after the event, but how does a complete stranger have access to a child's bedroom, with the child in the room, and time enough to complete a sexual assault?
I never allow workers in any room in my house without frequently popping in to see that they are working as they should be - usually under the guise of bringing them a drink, or having a chat about the job.
I no longer have any children at home - but if work was being done in their bedrooms, they would certainly not be present, and alone with the individual for one moment.