$ sudo apt install cowsay
the cowfiles should be here (ymmv)
$ ls /usr/share/cowsay/cows
there is an open bug for xmas-tree file missing, but have a look at the simple 'cow' file format and you can easily get the kids to make their own cow files
Code:
$ cowsay -f daemon Merry Christmas
_________________
< Merry Christmas >
-----------------
\ , ,
\ /( )`
\ \ \___ / |
/- _ `-/ '
(/\/ \ \ /\
/ / | ` \
O O ) / |
`-^--'`< '
(_.) _ ) /
`.___/` /
`-----' /
<----. __ / __ \
<----|====O)))==) \) /====
<----' `--' `.__,' \
| |
\ /
______( (_ / \______
,' ,-----' | \
`--{__________) \/
$ cowsay -f dragon Merry Christmas
_________________
< Merry Christmas >
-----------------
\ / \ //\
\ |\___/| / \// \\
/0 0 \__ / // | \ \
/ / \/_/ // | \ \
@_^_@'/ \/_ // | \ \
//_^_/ \/_ // | \ \
( //) | \/// | \ \
( / /) _|_ / ) // | \ _\
( // /) '/,_ _ _/ ( ; -. | _ _\.-~ .-~~~^-.
(( / / )) ,-{ _ `-.|.-~-. .~ `.
(( // / )) '/\ / ~-. _ .-~ .-~^-. \
(( /// )) `. { } / \ \
(( / )) .----~-.\ \-' .~ \ `. \^-.
///.----..> \ _ -~ `. ^-` ^-_
///-._ _ _ _ _ _ _}^ - - - - ~ ~-- ,.-~
/.-~