John bought 2 notebooks for his 3 children: 2 notebooks/child x 3 children = 6 notebooks. The father bought 6 notebooks.
John's wife bought 5 notebooks for their three children: 5 notebooks/child x 3 children = <<5*3=15>>15 notebooks. The mother bought 15 notebooks.
Now, the total number of notebooks is 6 notebooks +15 notebooks = <<6+15=21>>21 notebooks.
#### 21