divorce does impact a child this age, even though he will have no concept of what is really happening. Your son will pick up on your stress, sadness and anger, and may react to it by becoming more clingy, hyper or oppositional. This is a normal reaction because remember he only knows that something is wrong, and that is so scary to a little child. This is a time for lots of extra TLC.
Keep things the same as possible (your idea about the toys is important) and establish routines in both households (dinnertime, bedtime, bathtime, stories all of that should be as predictable as possible). Routines are very soothing to young children, and will help him adapt. The most critical factor will be for you both to avoid having any conflict in front of him. No arguing at drop-offs or fights when he is around! Keep things cordial and quick between you. Also do not things slide, like allowing him in your bed or feeling so guilty that you buy too many toys or stop enforcing rules. Finally, avoid exposing him to people you are dating, no matter how fun they are.
Professionals used to give the advice that children should be primarily with one parent, due to the belief that the mother was always the best caretaker for young children. I personally do not agree with this idea, and the research has not supported the notion that mothers having primary physical custody is necessarily the best thing. It is very important for the divorce not to cost him his relationship with either parent. A child in a joint custody situation does have extra stress, but with lots of love and attentive parenting he can be ok. You can expect tears at drop offs, and him saying he does not want to separate from whoever he is with. Let him express his feelings, give a quick hug, and then leave (just like you do at school). Then once the other parent is gone, find something to engage his attention so he can settle down.
You will want to be proactive to help him adjust as he grows. Each phase of development will bring new challenges. I recommend the book Difficult Questions Kids Ask and Are Afraid to Ask About Divorce by Dr. Meg Schneide. This is the best guide to helping kids through divorce I have found to date. You can also help your child adjust by seeking the help of a psychologist or counselor who specializes in young children. Some play therapy and parenting help can make the transition smoother and help you stay attuned to your little ones needs.
Thank you so much for your response it was full of great advise.