Sensory stuff - tubs of water and things in it - toys but also jugs, funnel, containers to fill and dump.
Trays of lentils with tractors etc in them. Trucks and stones. Gravel and buckets and wheelbarrows.
Sandpit - let the LO fill and dump but give the older more structure with making castles etc.
Out on wheels - big one on trike/bike/scooter, LO on ride on.
Simple colouring with crayons.
Play dough - again more structure for the eldest.
But basically I am thinking sensory stuff where the LO can fill, pour and dump, but the eldest can do more imaginative play. Dried beans and cupcake cases.
Is your younger one into filling bags etc and walking about??