Abel is five now and overheard Gemma "confessing" to his little brother Thomas about how killing their mother was a horrible "accident". This confession was brought on by Gemma being overcome with grief (and guilt) because SOA VP Bobby was killed as a result of Jax's plan to exact revenge on Tara's killer - who was id's by none other than Gemma.
After that Abel began acting up at school and smacked a classmate across the face unprovoked with his lunchbox. This was off camera of course. At home, Gemma was asking Abel why he did it. Abel said it was an "accident". Gemma asked Abel , "do you know what an accident is?" Abel replies, "Yes. Do you?"
In the latest incident last night he hurt himself and told the school and Jax that "Grandma" did it. School called social services and Jax had to take Abel back to his house to stay. Evidently, when Jax was putting Abel to bed, Abel spilled the beans.