Need tips for teaching 9 yrs old freestyle

Hi, My son is almost one month into swimming learning from a professional swimming coach. He is 9 yrs old. He is good in kicking and can cover 25 meters pool with his kickboard easily without any problem. Currently his coach is teaching him freestyle. He is progressing well but he is stuck at a particular point. He currently uses one arm swinging in water and one arm on the kickboard and breathes fine through side head but he is not going to next step from here on. The shallowest side of the pool is 4.5Ft and his feet do not touch the bottom and he is scared to swimming without kickboard. He can hold my hand and can swim with kicking easily but he still needs someone's hand or some support on his front. His coach tried to encourage him go swimming with his kicks and his arms straightened but hardly covers 10 feet with this and goes down. What can be done here? Should he use hand paddles? Any swimming accessory which could help here? Kind Regards, Khabbab