As Johnny and his son are humans, and humans walk on two legs, this means that between the two of them there are 2*2=<<2*2=4>>4 legs' worth of organisms.
There are two dogs walking along as well, and since dogs walk on 4 legs this means there are 2*4=<<2*4=8>>8 legs' worth of organisms.
We add these two totals together to find there are 4+8=<<4+8=12>>12 legs' worth of organisms in total.
#### 12