Here are the suitable words to complete the passage:

1. **brings** - "It is believed that tree brings the Christmas spirit inside the house."
2. **allowed** - "Gifts are placed under the trees and they are not allowed to open till the eve of Christmas."
3. **cooked** - "Special food is cooked in every house."

So, the completed passage reads:

"This event brings a lot of happiness for kids. Families usually decorate their houses with lighting and flowers. The place is usually decorated with Christmas tree. It is believed that tree brings the Christmas spirit inside the house. Gifts are placed under the trees and they are not allowed to open till the eve of Christmas. We write cards for their loved ones. Families spend a lot on this event. Special food is cooked in every house. It includes homemade pan cakes, plum cakes."