When Mehr is negotiated, no one knows how many children would be born, what will be their needs (healthy, sick, disabled) or at what stage in future the divorce might happen (young, teenager, earning children).Technically the Mehr is the socio-economic enablement just for the wife but she may do with it as she pleases including say setting up a business fund ( if the Mehr is money and is paid during the wedding and she has saved it ) for her children.
The OP has this :
So I think in this particular nikahnama ( marriage contract ) the future children's rights were separately arranged other than the house in her name.
How will the Mehr decide the right amount for children in advance then?