I have a 6yr old son who I've known for a while now that something is wrong
I would call a regional children's hospital. You should find one in any fairly large city. Ask for the Child Development Department. There will be a team of child neuropsychologists, psychiatrists, and social workers.
The other possibility (but it would be my second choice) is a major university medical school. Their Pediatric Department. Your pediatrician is a good place to start. You can ask for referrals. (But insufficient, I think.) If there will be a long delay for an appointment, I would look for alternatives, and I might ask for a referral to a child neurologist in the interim.
Something could be going on in terms of physical health or specifically neurologically that confuses and bothers your child, that he misinterprets--and propels him to act out. In any event, he requires further diagnosis. Or there could be a yet undiagnosed developmental disorder, or even what some parents refer to as atypical "hard-wiring." It is not that uncommon and there are interventions.
I would do this as rapidly as I can. First, you suggest your daughter may be at risk. While a child that age cannot formulate intent in the way an older child and adult can, it cannot be good for anybody, him, you, your daughter, for this to be allowed to continue.
I would start making a list now of all of your concerns, and I would carry around a tablet and note what happens each day. Try to be as detailed as possible noting the time of occurrence, what your child is doing, who he is with, and if you see a trigger, note that.
Start logging everything your child eats, their sleep habits, bedtime, waking, etc. Anything you can think of. You will begin to see patterns, and you will be able to summarize succinctly your concerns to inform the professionals.
Your child is school age. What does school say? I would think about requesting an evaluation by the school psychologist, but I think I might wait, if I could until you have your own evaluation. Special education status is what you want to establish for your child and an IEP (which is an intervention plan.) ADD alone is a qualifying diagnosis.
Your child, based upon what you describe, should qualify for school-based services and interventions.
I am sorry you find yourself here. But you will find some good help and support. Remember. Those of us here cannot diagnosis. We are guided only by our own experience. Your best bet is expert and qualified professional help, as above. Take care.