maybe when parents gave the house children and in agreemant ( in donation) was that children had to take care about parents, until their death.
No, it had NOTHING to do with a promissory undertaking about a house. This is simply and purely based on the fact, that now as children have a better lifestyle than their parents, they should look after the 'less well off parents'. The State supports this, as otherwise the State picks up the bill. Seems strange, but true.
In fact, if a parent is kicked out of a rented flat, the State can, if the child has sufficient space/room ask the child to look after the parent.