Vasubaras marks the beginning of Diwali festival. On this day, Cow and her calf is worshipped. A small pooja is performed for the Cow and calf and they are fed Karanji. Karanji is a sweet prepared specially for Diwali festival. It is believed that no one in the family should eat Karanji before it is fed to the Holy Cow. Some ladies also fast on this day and consume meal only once.
In a legend, it is mentioned that from the Great Churning of the ocean (samudramanthan) five wish-fulfilling cows (kâmadhenûs) emerged. Among these five wish-fulfilling cows, a divine cow Nandâ had also emerged. This vowed religious observance is performed to worship this divine cow Nandâ. On this day, married women (soubhâgyava¬tîs) undertake a fast partaking of only one meal, and either in the morning or evening; worship an embellished cow and her calf. (source: http://forumforhinduawakening.org)
Vasubaras is also known as Govatsa Dwadashi. According to Hindu Calendar, this day is celebrated one day prior to Dhanteras. I fill post information about Dhanteras in due course of time. Since Hindu calendar something called as “tithies” (similar to dates in English Calendar), the actual dates keep changing each month but the Hindu month and tithie is the same each year. This is true for each festival. For example, in the year 2015, Vasubaras fell on 7th November while this year it is on 26th October, but in both the years Hindu Calendar month and tithie is the same – Ashwin Govatsa Dwadashi
While you share this significance with children to inculcate traditions and rituals in them, do help them to relate to today’s world. They might not want to know the dates and tithies of this festival but the lesson that they need to know is – worship some power (Cow in this case because it is believed that she houses 33 crore Gods in her body), pay respect even to animals, feed them, learn to sacrifice (in this case – one meal). Take your children along with you when you perform this pooja and if it is not feasible to do so share some pictures with them. In the end, they should learn to be respectful, caring, giving & surrendering to God/Pious power.
Do add whatever information you have about Vasubaras, I would love to learn more!