How about a messy play area with gloop, shaving foam or hand painting, or use jelly and thick custard, that way you know they wont come to any harm, unless they have any allergies.
obviously due to the age and always putting things in their mouth this area would need constant supervision.
Playdough to encourage fine motor skills and encourage them to manipulate and play with new textures.
A physical play area encouraging gross motor skills, balls, beanbags, small hoops.
A sand box with sieves, cups and funnells.
P.S I like the idea of your welsh wall, I am welsh - a taffy x
Good luck