Back in the 1930s and 40s, the Blondie & Dagwood films were very popular....so popular they made 28 of them!! Not surprisingly, about a decade later, they tried a television version but it only lasted a single season. Oddly, they made it without any of the original cast other than Arthur Lake (Dagwood)...and Penny Singleton was replaced by Pamela Britton ("My Favorite Martian") and Mr. Dithers (who was played by a couple different actors in the films) was replaced as well. Now it did make sense to re-cast the kids...as by now the originals were just too old to play the parts.
I don't think the series failed because of the new cast. Instead, I think it was the inconsistencies in the writing. The episodes ranged from excellent to terrible...and I am sure this didn't help the show! My biggest complaint is that some of the shows portrayed characters in a mean-spirited manner....which is crazy, as the charm of the films were the nice characters. In one episode, for example, in "Husbands Once Removed", Blondie convinces Dagwood they aren't married and makes him pay rent and cuts him off physically and emotionally....even though he'd done nothing wrong and was generally a wonderful husband! She just wanted to 'keep him on his toes'....and she seemed really mean in this one. Likewise, in "Follow That Man", Mr. Dithers thinks Dagwood is embezzling from him!! I can only assume they ran out of ideas and the series had pretty much run its course. Worth seeing if you can find the DVD set but certainly not as lovable as the films.