Letting Go. To Ride the Bus or Not To Ride

My son and daughter to about to attend their first public school.  I have a soon to be first grader and kindergartner. The school strongly encourages using the school busing available for transportation.  I'm petrified thinking of my little 5 year old on a bus for 45 mins.  How in the world am I going let them ride the bus?  Huge transition for Me and them.  I may need to ease into this, a bit.  Maybe I'll drive them the first couple of weeks and then let them get excited about riding versus bartering with them about it.   I'm so nervous!