My son doesn't believe in Santa, but his older sister does. I'm not telling either of them the truth.

• My son is 6, and my daughter is 9 and they can't agree on whether Santa is real
• At a mall, they both asked me which one was true, whether Santa was real or not.
• I told them he lives in your hearts because I didn't want to tell her the truth.

Walking past yet another mall Santa during the Christmas shopping season, my 6-year-old son wondered aloud, "I don't think that is actually Santa. How could he be in so many places at once?"

My 9-year-old daughter, without missing a beat, announced, "That's him. That's Santa. I know it is."

I could see what their brains were doing. My son was growing up, piecing something together, and standing on the cusp of an older version of childhood, and seemed moments away from figuring it out. My daughter, however, was fighting a very different battle: a desire to stay young.

I knew this day would come

Both of my children have tender hearts — crying if the wind blows too hard or at a particularly moving scene in a "PAW Patrol" movie — but my daughter has always been acutely aware that she is aging. When she was a toddler, she would tear up at pictures of herself as a baby, nostalgic for a time she didn't even remember.

I knew this day would come, but I couldn't have been more wrong about how it would play out. I have learned, though, that the vast majority of the time, when I plan or worry about something, I am usually wildly off-base. So, I try to exercise the kind of mindfulness I have learned as a mother: to take in the growth of my children one day at a time. Do not make plans, I tell myself, for what might not even happen.

I could sense, though, walking through the mall, my children wanted only to intensify this conversation. My son pointed out all of the Santas we have seen, while my daughter, in her increasing frustration, kept saying, "Well yeah, that's how Santa works!" By the time we got to the car, they were practically screaming at each other, and when they both turned to look at me, I knew what was coming.

"Santa's not real, right Mommy?" my son asked.

"Yes, he is. Tell him he is real, Mommy," my daughter said, tears in her eyes.

She's such a sensitive child

I know when my daughter and I go for walks every night with our dog in our neighborhood to steer her away from the litter of kittens we have seen frolicking in the doorway of an old barn. She is worried they don't have a mother and no one will take care of them in the winter.

She is so sensitive she used to cry when we took the books back to the library. She is also a straight-A student, tests off the charts, and is enrolled in the gifted class for language arts at her school.

When we play board games, checkers, or Mario Party, I no longer go easy on her since she is so strategic she usually beats me. Her mind is a whirling dreamscape that allows her to write stories full of far-fetched ideas interlaced with similes, metaphors, and unique perspectives I would kill to have in my own writing. For most of her life, she thought IHOP was a chain of trampoline parks.

I think she knows the truth

"Santa lives in your hearts," I said.

They looked at me, a little stunned, taking this in, but they seemed satisfied. My son literally shrugged, and my daughter looked visibly relieved. We got in the car, and the conversation drifted elsewhere. We discussed dinner plans, what characters we were going to be in Mario Party, and whether it really was essential for them to bathe as often as I requested.

I suspect she knows the truth, the same way she knew COVID-19 was happening. I hadn't told her, but I gathered she figured it out a few nights into the first lockdown when she looked up at me and whispered, "I feel like there's a monster outside." I didn't tell her the truth then either: it's not one, but many, and there will come times when you have to fight so hard, harder than you ever possible, for what you believe is right in your heart.