Tear down the old "shed" or leave it standing?

Leave it as is! So what? As long as no one is endangered by falling parts, there is no need to invest anything. If in 20 years your mother or daughter is looking for an apartment, a change of use in the outdoor area is easier to approve than a new building.

Thanks also for your opinion! That is basically of course a good point! The thing is, my mother already lives with us anyway. We have a 220 sqm house. After the renovation, which will take place soon, she will have about 90 sqm and we will have 130 sqm available. You are probably right about the children too. Hmm. That would definitely be an argument. My line of thought was also a bit that when sitting on the terrace, you can keep an eye on the children if they are playing in the garden. But those are the first years anyway, and they don't play somewhere far away from us for hours. And later they will be glad not to have to see us.