just about moved in.

Was Sudsy canned so that Chip's brother could get work?

In this interview

https://www.youtube.com/watch?v=KmKbMP5-7-E

Stanley Livingston relates that Ricky Allen (who played the role) was a hockey player and got injured (I think he said Ricky lost some teeth). Thus, no more Sudsy.

Ricky Allen returns much later on, just 2 times (total) in Seasons 7 and 10, playing different characters. He missed Seasons 4, 5, 6, 8, 9, 11, and 12 entirely.

In my opinion, having grown obviously, he's pretty much unrecognizable in those 2 appearances as compared to how he'd looked as Sudsy.

Like his brother Stan, Barry "Ernie" Livingston had experience working on The Adventures of Ozzie and Harriet, so his selection when M3S was in need of a very young actor must have been more than a little obvious.