What is the relation between stateful and stateless widgets in Flutter?
A StatelessWidget will never rebuild by itself (but can from external events). A StatefulWidget can. That is the golden rule.
BUT any kind of widget can be repainted any times.
Stateless only means that all of its properties are immutable and that the only way to change them is to create a new instance of that widget. It doesn't e.g. lock the widget tree.
But you shouldn't care about what's the type of your children. It doesn't have any impact on you.
From the documentation at flutter.io:
...The important thing to note here is at the core both Stateless and Stateful widgets behave the same. They rebuild every frame, the difference is the StatefulWidget has a State object which stores state data across frames and restores it.
If you are in doubt, then always remember this rule: If a widget changes (the user interacts with it, for example) it’s stateful. However, if a child is reacting to change, the containing parent can still be a Stateless widget if the parent doesn’t react to change.
As mention in flutter docs
What’s the point?
Some widgets are stateful, and some are stateless.If a widget changes—the user interacts with it, for example—it’s stateful.A widget’s state consists of values that can change, like a slider’s current value or whether a checkbox is checked.A widget’s state is stored in a State object, separating the widget’s state from its appearance.When the widget’s state changes, the state object calls setState(), telling the framework to redraw the widget.
A stateless widget has no internal state to manage. Icon, IconButton, and Text are examples of stateless widgets, which subclass StatelessWidget.
A stateful widget is dynamic. The user can interact with a stateful widget (by typing into a form, or moving a slider, for example), or it changes over time (perhaps a data feed causes the UI to update). Checkbox, Radio, Slider, InkWell, Form, and TextField are examples of stateful widgets, which subclass StatefulWidget.
https://flutter.io/tutorials/interactive/#stateful-stateless