I think that both of them are 擬音語(echoic word). generally, ルラ ルラ ルラ is the image that a person is happily humming, チータカタッタッタ is the image that a person is having fun with a musical performance by some instruments. I tried to check the actual intention of the song's writer using the internet, but I couldn't find the song's writer's comments about this song.