My preschooler keeps giving the baby a name nobody agreed to

Our new baby's name is Benjamin. My four-year-old calls him Pickle.

At first everybody thought this was funny. She announced that he looked like a Pickle, made him a picture with a green circle on it, and told our neighbor that Pickle was home.

Now my mother calls him Pickle. My husband has started saying it absentmindedly. I heard myself say “Pickle's blanket” yesterday and felt ridiculous for being annoyed.

We spent months choosing Benjamin. I don't need everybody to use the full name every time, but I would like his actual name to survive the first month in our house.

My daughter says Benjamin is his grown-up name and Pickle is his name here. When I corrected her in front of my mother, she looked at the drawing on the refrigerator and asked if she had to take it down.

That was not remotely what I meant.

I don't want to turn her silly nickname into a mistake. She seems pleased to have contributed something to all the baby preparations that happened around her. She didn't choose the crib or the car seat or his name. She chose a green circle.

But I also don't want to hear this nickname every day simply because objecting makes me seem humorless. My husband says it will probably disappear on its own. Maybe it will. That doesn't change the fact that the adults are doing most of the repeating.

There are two separate things here, and I keep aiming my frustration at the smaller person. My daughter can have her goofy name for her brother. The adults can also use the name we gave him.

I put her drawing back after changing the refrigerator photos. She checked that it was still there.

Would it be petty to tell the grown-ups I want more Benjamin and less Pickle? I can tolerate an occasional nickname. I think what bothers me is being expected to love it just because the origin is cute. I'd like to keep her contribution without surrendering every conversation about my son to a vegetable.