I know you’ll all think I’m nuts but I love this cartoon and the theme as well. It’s just awesome. I transcribed the lyrics myself.

SHIN CHAN!
Ending theme

Woke up late this morning
clouds were really rolling
frogs and dogs were raining from the sky

everything seems awkward to me
nothing’s just as it should be
if this keeps up i surely won’t get by

and then i close my eyes and try to smile
i know things are bad and getting worse
but after all this i can rest a while
and then i’ll party party!

Party party!
Join us join us!
Party party!
Join us join us!
Party party!
Join us join us!
Shake your tail and you can
Party party!
Join us join us!
Party party!
Join us join us!
Party party!
Join us join us!
Shake your blues away!

Yo, reggae vacation mon!
this party’s shakin’ and it aint just shakin’ me
i see you smilin’ grinnin’ ear to ear
sing the song and you should really sing it clear
just sing along with us!

Party party!
Join us join us!
Party party!
Join us join us!
Party party!
Join us join us!
Shake your tail and you can
Party party!
Party party!
Party party!

Here is the adultswim.com page for Shin Chan, and at the right side under extras you can click “Party, Party, Join Us, Join Us” and listen to the song, as well as view the end titles. There’s at least one episode up for grabs as well.