All kinds of things! I read aloud a lot to both of them. My preschooler enjoys drawing and colouring, and sometimes I will sit and draw with her. We also do craft stuff, like making things out of paper plates and egg cartons etc. Baking together is fun too, as is painting each others' nails. The toddler likes it if I sing him songs and nursery rhymes, and sometimes his big sister will join in.
The preschooler loves going to the museum and art gallery and they both enjoy a music session at the local church. Outdoors they like going for walks and "nature hunts", visiting parks and playgrounds, riding tricycles... All the classic kid stuff really.