Juvenile Court: Minor in Possession and Evading Arrest

My question involves juvenile law in the State of: TX

My son was at a party at about 11 at night, and walked out of the house to go home with a red SOLO cup in his hand. He was in another person's lawn across the street with his back faced to the house where the party was taking place when a police officer said that he appeared to be urinating and went up to go talk to him. Immediately, my son threw the cup down and ran down the street, where three officers threatened to taze him and proceeded to tackle him to the ground and hit him with their baton. My son was charged with Evading Arrest and Minor in Consumption. When tackled to the ground, his knees got scraped up and they smashed his head on the ground, leaving a gash that was bloody enough to where EMS was called. Also, when searching his person, they found his fake ID, which he had told them that he was in possession of, and so they didn't charge him with that. He was handcuffed and taken to JUVI, and was booked, however, the nurse would not take him due to his injury, so he was taken to the nearest hospital via Ambulance for his gashed head. Then, he was released into my custody. My question is "Did my son have to stop and talk to the police officer, even though he had a cup in his hand and "appeared to be urinating"? If he was really urinating, they would have charged him with a completely different crime. Also, was this a use of excessive force? He was the only one arrested or cited at the scene of the party. Also, can he still be charged for his Fake ID, even though the officer initially didn't charge him for it? It has been a week and a day, and he was never read his Miranda rights.