I make a division between "age-regressed Turtles episodes from the OT" and "Flashbacks to when the Turtles were actual children". The former are mediocre cartoon episodes that are forgettable, and the latter are important for character-building.
The biggest problem I have with the first type is that they're a "what might have been". I still think of OT Splinter as fatherly, but have to admit, having the Turtles start out their sapient life as small children that he had to take care of probably gets the "fatherly" theme across to the audience better. Plus, it's super-cute when in the right hands.
The OT skips over that and has them become "teenagers" right when they mutate (don't ask me how that works...), so there's a lost opportunity there. The Archie comics retconned this scenario so that Splinter still had to raise the young Turtles, and was better for it.
So, looking at the age-regression episodes of the OT, I feel a sense of disappointment that we got that, instead of the for-real young Turtles to showcase their familial bond.