The only motor museum I can think of was down Pembrokeshire way,if it still open.
St Fagans near Cardiff should be interesting for all ages.
This site consists of Historic buildings that have been dismantled and reassembeled Brick by Brick from all over Wales.
Including shops,chapels,churches,houses of all sorts.
And of course entrance to most museums are free here in Wales,unless privately owned.
Jethro