Why does cold air come up from my heating registers before the hot air comes out?

The air in the ducting through out the house must go some where and has not been heated through the heating system yet. The cold air should not last long at all. If the cold air is longer than a minuite than you may have a problem with the heating coiles in your furnace.

Because the pipes (ductwork) are full of air at the same temperature of where they are located, i.e.. Crawlspace/attic. That air blows out before the treated air comes through.

This is the air that is in the ducts when the furnace starts up then is blown out into the room.

There are in the crawl space... should I insulate around them... thanks again for your help!

By all means insulate them. You can also keep the room air blower on all the time. This will blend the temperature in the house but will use more electricity to use.