People who thinks that the anime is 'kiddish' needs to define better what they really mean by this statement, and what categorizes it into 'kiddish'.
The anime has always been for a younger age group, and its not going to change. Moreover, it shouldn't.
To be honest, the anime only needs a few improvements, like a revision and a little more detailing of plot and expanding the other characters which are barely touched. Other than that, I think the anime is just good as it is.
The Kanto episodes were great to me just because they were light and dealt with humor more.
The last thing the anime needs is death, violent battling, and pondering the meaning of life.
Even when I was a kid, it was an escape from real life, and it should stay that way.
All that it needs is more detailing with the overlooked parts of the anime.