However, a returning resident permit is considered prima facie intent to retain residence so it might be a good idea to get one before you leave. Although a returning resident permit will help counter an allegation that you have abandoned permanent residence, it will not preserve continuous residence for naturalization purposes . In some situations, you can take steps to preserve continuous residence for naturalization, but I will not discuss them here. You may wish to consider acquiring your U.S. citizenship before you leave the United States. You will not lose your Canadian citizenship if you do.
Dual citizenship is recognized in both the U.S. and Canada.
If your Canadian born son is the natural child of your U.S. citizen husband, he may have acquired U.S. citizenship through birth abroad. However, I don't know enough about the facts to advise you on that matter. Your daughter is a U.S. citizen but, as your child, she may also have a claim to Canadian citizenship. No formal registration of birth abroad is required. All rights reserved.