every now and then, time moves so quickly!

In a week and a half, Bigguy turns four. It doesn't seem like four years since he has been born, yet it was June 23, 2001, just before midnight, that he made his appearance in this world. Bugguy is very intelligent and likes to use big words, like vehicles and edible, instead of saying cars and trucks and planes, and can be eaten. I worry that as he grows older he will lose some of his properrnes and nit-pickyness that seems so unique right now. He also has a very refined pallat. He likes bleu cheese, and greek food, all vegetables, thai food, and had junior sushi last night(no fish or wasabi, but Eda Mame, egg custard, sea weed...he liked it.) He loves jazz music, word games, dancing, and moving his body to his emotions, ("Momma, this is how happy looks, this is how angry walks, this is how silly wiggles...See Momma, my body moves with my feelings and emotions, Here is confused, this is hungry...") I want him to be this innocent and open forever, I never want him to be ridiculed for being who he is, even if that person is rather different, and kind of obbsesive compulsive about very random seeming things. I want him to remain the boy who gets excited to the point of giggling when he figures out how something works. I want him to keep the drive that makes him figure out how things work in the first place.
"Look, Momma! The wheels on the train have a long rod that connects them at different places, that's how the wheels all go at the same speed so the train doesn't trip!"
"Poppa, I made your computer so it can run two things at once!"(a very exciting revalation for Bigguy)
"Momma, Littleman has teeth, so now he can start eating some food like me, and I can share with him, because his teeth will help him chew!"
the down side to having such an intelligent, sensitive, perceptive child is evident as well...
"Momma, are you sad because grandpa and grandma step-mom didn't call again."
"Momma, I have grandparents, how come you don't-do you miss them?"
"Poppa, where is your poppa, and how come we don't have pictures?"
"Poppa, will momma's daddy not be at my birthday again, like last year?"
How do I explain this to him, that we don't know who hubby's dad is, that my dad and step-mom are being pricks right now, and unfortunately, he got drawn into it, that eventually, grandparents die? I want him to hold on to his innocense for as long a possible, but at the same time, he will have to make and find his own truths in the world, and with that, the inocense andchild like sense of wonder can be lost.