Congratulations!
I became the father of six at age 46. The youngest was two when I came on the scene.
The journey is not always what you think it will or should be, but what a ride...
I'm into the grandkid phase now as well and hope to introduce then to trail-a-bikes in the near future.
I can still remember when my youngest was three and he decided to get off the trail-a-bike when we we going about 5-10 miles per hour. He survived, but never did that again. I can also remember getting him his first bike helmet and watching him do a headder onto the helmet on his trike at age two. Didn't even phase him... Never forget the helmets and other safety gear.
You have a lot to look forward to!