My ds is 3 (4 in feb) all he ever asks for is cars, trains or planes.... our house is full to bursting with this stuff so id like to buy him some different bits, he has a great little imagination so im thinking playsets like happyland or little people BUT im worried he is too old for these kinds of things, he seems to get frustrated with the small fiddly bits on playmobil... duplo? Do 3 year olds like that?