dad's truck vs. grandpa's truck

as a kid, i wanted so badly to be inside my dad's 18 wheeler.  he often came home for lunches- leaving it parked but running in the center of the culdesac.  i almost always asked but the answer was always a firm 'no'... a temptation parked within reach. 
fast forward a few years- routine still in tact- same dad (aka grandpa) comes home for lunch and the question asked this time by grandkids is answered with an easy "yes!"...  yes!???!  yes????