thanks everyone, plenty to think about now
The paints will show up any imperfections in the walls. So expect to spend time sanding or filling to get flat wall. The paint will not cover cracks.
The paint can mark with furniture against it or scraps from wood etc, and it’s not a good idea to remove marks with a wet sponge and rub at it for example. This puts it as non child abuse tolerant - the paint is chalk finish.
This is a concern, the walls are not perfect. We damp proof work down and the whole downstairs replastered to a height of 1m (didn't want to do the whole walls as it'd mean removing dado rails, and fancy plaster above dado rail / cornices etc). Initially we could paint this new plaster with breathable paint - there's still a visible join in the old plaster. I think it'd need smoothing and then using lining paper to get it all flat.
Also.. we're going to need it child proof really - daughter is only 7 weeks at the moment, but won't be long before she's ruining the walls, nice carpets and the lovely leather sofas!