Until the beginning of the 20th century, village children younger than 8 years old (both boys and girls) wore alkle-long
pure-white shirts. Those shirts often were altered from parents' clothes.A practical reasoning is obvious here: a child grows fast (on the one hand), and (on the other hand) he/she wears his/her clothes carelessly - so there is no point to make child's outfit of any expensive cloth, or to decorate it with hard-to-make (handmade!) embroidery. But, there is a spiritual explanation too: in accordance with Christian (and pagan) opinion, a child is innocent, and Heaven's white light shines above him/her yet. So, his/her costume suppose to be pure white, with no any marks of an earth's life.
However, now our lifestyle is different. Traditional outfit is not an everyday clothes for us anymore. It became just... just costume for special occasions. Therefore we decided not to follow the tradition literally, but to keep the ideas our ancestors had about children's clothes instead. Couple of centuries ago, the cheapest cloth available for peasants was home-made linen. It was of a creamy-white color. Now, for us, the cheapest fabrics is cotton (and dark colors are the most suitable for kids). Besides, we add red details to this shirt, to make it nicer (despite the fact that
"fire" trim and "fire chest shield" on shirts traditionally appeared no earlier than at teen ages).