The children's room is too warm in the new building.

Did you check the valves?

?

Because I currently live in the house with my wife and a 2-year-old child and don't just want to mess around with the heating.

You don’t mess around, you try things out! Have you studied the user manual?

never touch a running system!

But your system doesn’t work.

What I'm still interested in is whether it makes sense for the temperature to be capped at a maximum of 35 degrees?

What do you mean by that? Is it a setting or your observation?

What kind of heating system is it actually?

1.1 has an endpoint of 65 degrees flow temperature at -15 degrees outside temperature. That is a setting for a gas burner in a 90s house with radiators. Who set that?
Happy sweating. No wonder the floors become noticeably warm.
Reducing to 35 degrees only helps to a limited extent. With the heating curve, this is already reached at around 10 degrees outside temperature. So the heating is already simmering during the transition period and the room thermostats dutifully keep their mouths tightly shut. When they do open, it gets very warm at the feet ...

I have now set the curve to 0.4 and want to observe the whole thing. If everything stays nice and warm, except for the floor, then I want to set it to 0.35.

It is a Vaillant underfloor heating.

What do you mean by that? Is that a setting or your observation?

It is set that way.

It is set that way.

Sounds reasonable. If the heating curve is set correctly, then this setting becomes irrelevant.