Do you 'try' and get them 'into' anything...or just take their lead?
Example - 3.6 yr DS old not really into anything (not interested in building, colouring, crafts, vehicles, sport) except a big talker, bit of cooking (10 min limit attention span), bit of TV after nursery in mornings only just starting to play imaginative play (v limited involving a scenario, not with any toys just 'You be the baddie, I'm the goodie')...