Splatoon - Some wear it better than others...

Octodad for DLC in Splatoon.
Make it happen.

Crazy theory:
The mom from octodad was secretly an Inkling all along. More specifically, an inking large and skilled enough to perfectly shape-shift into a fully grown adult human. She only pretended not to notice the fact that octodad was not an octopus, since she was (almost) a similar creature: a squid, thus she was able to identify octodad right away.
Since neither a human or an inkling is able to breed with an octopus, she somehow gave birth to 2 children, most likely from a form of asexual reproduction. This means that both the children are completely inklings.
If we are to believe that Octodad takes place in present day, and Splatoon in the not-too-far future…