Simplify the following text for a Grade 10 native English-speaking person.
Original: Development for both The Lightning Thief and the Percy Jackson series began when Riordan began making stories for his son Haley who had been diagnosed with ADHD and dyslexia .
Simplified: Planning for both The Lightning Thief and the series began when Riordan started making up stories for his son , Haley , who was found to have ADHD and dyslexia a short time before .