I'm not aware of any thought disorder questionnaires for children, but PIC-2 (Personality Inventory for Children-2) has a section or two on hallucination and reality.
The popular CBCL (Child Behavior Checklist) has a few questions on thought disorder.
You might check out NIMH, which has the Diagnostic Interview Schedule for Children, IV, which includes questions about psychosis. There are many online references to this, and a manual at https://www.cdc.gov/nchs/data/nhanes/limited_access/interviewer_manual.pdf