Regarding the original question, there is no convenient way of lifting a parameter to a higher level, so you do have to resort to manual work like you did:
model son
parameter Modelica.SIunits.Angle k;
Modelica.Blocks.Sources.Constant const(y(unit = "rad"), k(unit = "rad", displayUnit = "deg") = k) annotation(Placement(visible = true, transformation(origin = {-20, 20}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
end son;
However, you can do deep modifications. If you double click on son in screenshot 2 and select the constant block you can set a value for k. In Modelica code that would look like this:
model father
son son1(const.k = 5);
end father;