To be the new kid on the block means to be new to the area in which you have just moved or to be new to a group that you have just joined.
1. The Scouts group leader had to explain the different rope knots to Shahid as he was a new kid on the block.
2. The Gandhis took it upon themselves to give a warm welcome to the Desais as they were new kids on the block.
3. The Senior Manager took the young trainee under her wing on his very first day at work as he was the new kid on the block.