How do I bathroom / kitchen / extension? etc.

I laid some rubber floor in our utility and it’s quite bouncy. Yet to check how well a baby bounces but defo softer than concrete.

You could go this way, screet/concrete and whilst the kids are young stick on some marmoleum.
Once the fontanels are sufficiently joined, rip out the plastic garbage, polish, beautiful floor.
Nice concrete pavement outside, outside and inside are the same but different.

Surely all floors are hard?

Not really.

Concrete is especially hard. As in you need to wear slippers hard. All dropped things break hard.

I went to a nice flat in the Barbican a while back and it was some sort of vinyl rubber stuff. Shoes had to be removed and it was so lovely to walk on.

I feel that concrete and kids is only viable if don't have custody.

Looks good tho.