Children often love to see adults dressing and expressing in ways that are unique and fun. It brings them joy when they see trans people do this.
What is more important than creating opportunities for children to feel joy? This is also why drag story hour events are so beneficial to children (whether the performer identifies as trans or not). Obviously children are going to be more likely to learn how to read when the teachers are wearing fabulous and sparkly outfits!
In a culture where gender norms are often rooted in a lot of oppression and harm, trans adults help children to imagine a future that's outside of harmful power dynamics.
It can be surprising the ways that children internalize stories about what boys and girls "should do". Often these stories cause girls to feel bad about their looks and expression, while causing boys to feel ashamed for having natural human emotions. Nonbinary and trans children often face the biggest impacts of this. It can be powerful for children to learn that these harmful stories are not true. Seeing trans people living openly helps children to imagine other ways of living.
Trans adults often have a very important perspective on how to find joy in really difficult situations, children need that now more than ever.
Times are tough right now and children are feeling it. Many trans adults have experienced a lot of adversity and still found a way to love themselves and find joy. Children need that support as well. Trans people provide a unique perspective that can help children to become more resilient.
I've seen how children always benefit from seeing a range of adults from various backgrounds and experiences. We owe that to the next generation, So they can help us to evolve.
Of course, trans people aren't the only group of people with wisdom to share with children. From my time working with children and studying mental health, I have seen how children really thrive when they are able to see adults from a lot of different backgrounds and experiences. Showing children there is not one "right way" to think helps children to learn how to problem solve and think for themselves.