Wht don't you put padding and margin features in FlexContatiner(not child)?

[cplus98]

It is more efficient than using a separate MarginContainer because it is processed at once when calculating FlexContaminer layout.

[citizenll]

Due to the initial design, I defined FlexContainer as a Container node in Godot, following the behavior of Container. MarginContainer node handles the margin itself, and currently neither the container nor its child nodes have padding. This can be added as a new property to both the container and its child nodes (padding handling is available in version 3.5).