The older unnamed child may be getting jealous of his sister doing the prayers at bedtime. There has been friction as to how the Trisagion prayers would be divvied up each night.
The older child has gotten one up on the younger. Except for singing “O Heavenly King” as the introduction to the prayers, they have otherwise heretofore been spoken. Well, the younger child may be able to do subtraction and multiplication at the age of three, but she’s never tried plain chant. The older child started chanting “Most Holy Trinity. . .” and didn’t stop until “O come let us worship and bow down. . .” He turfed his sister out. She was not well pleased.