Help with a defiant child

I have 7 children ranging in ages from 27 to 4. My youngest is about to have his birthday party and has become most defiant. More so than any of my others.Now I should mention this child was in a car accident caused by a drunk driver and watched his cousin bleed to death and his sister has permanently been disabled, while he and his older brother were basically unharmed. So we have had him in therapy for behavior, but his defiance had become out of control.Being so young we have tried time out, temporarily taking his privileges, but today he started hitting everyone in the house. He got upset that one of his toys batteries died and as I was changing them he had a full on tantrum. My husband thinks we need to cancel his birthday party next week. It’s a drive by but it’s still a big deal. His therapist thinks this phase of life will pass as he processed the trauma, but in the short term he needs consequences for his actions. Any advice would be appreciated! via /r/Parenting https://ift.tt/3m3EOLi