My brother was 2,and I was 6 when our parents divorced. My mother actually took me to a beach house for the weekend, so that my dad could pack up his things at our house. She told me there that things would be different when we came back home. She explained that my dad would not be living with us anymore, that he will be living in his own home, and we would be living with her in ours. She said that we would see our father whenever we wanted. She basically explained that we would always be a family, however, they would not be married anymore.
At 6, you can't really process everything all at once. It was difficult to understand, however, my mother explained it the best way she knew how. I was always a very sensitive child, and new something was off with them.
Anyways, don't think that your son doesn't know what is going on, either. Kids are very intuitive, and observe things well enough. It's best to explain everything to them as best you can , and to not leave them in the dark. They will start to think it is all their fault, and grow up very confused, as well as have behavioral issues.
I would suggest finding a child psychologist during the transition period. Having someone talk to them, as well as you will be beneficial. It will keep them from feeling neglected, in the dark, and that their feelings matter. having someone they can talk to, trust, and know that they aren't the reason why this is going on, is just so important. In my opinion, you and your husband decided to change your family, not your children. Your decision will effect them long term. It would be extremely selfish on your end to not provide a service to your kids during this time. I am sure any place would also offer financial assistance if needed.
I say this as a person who came from a divorced family. It was not an easy thing to go through, and you never really get over your family being different. Sure you move on, they move on with other people, but it changes you. It also is worse when the children are younger, because they don't understand it enough to process and deal with it. It changes their character, personality, and their views about relationships in general.