Some just have a tough time writing it all the time. Others get made fun of.
someone long ago said, I want my last name to be...
Assuming you mean the names of both parents and their children, I would sign it as: John and Jane Doe, and children, Judy, Alice, Bill and Joe, want to wish you a happy holiday season.
If the boy is four years old he is probably used to using just his forename, not his last name. Nursery school workers etc do not usually use children's last names (ie surnames) when they are talking to children. If you and your boy have different last names, that would probably cause more difficulties later in life. People would want to know why you and he have different last names and that could be an invasion of your and his privacy.
Why do you want to know
Parents can call their children whatever they want. Regardless of what they've changed their names to, they're still their children.
I am not sure exactly how long they will last, but they will last for at least 1 year.
for as long as you want....?
As long as they want it to.
Most parents do this because they want their children to have unique names and stand out. Or they could choose the name because they like the name.
Safaris with Africa Travel last as long as you want them to last. It all depends on how long you want to go for. Obviously, the longer the safari, the more it costs.
How ever long you want it to last.
As long as they want it to.