The Hungries food chain
Monsters, as we all know, come in many different shapes and flavours. The Hungries are monsters of the simple, friendly kind that every child can relate to: just by making them ‘eat’ things, using their sound behaviours and adding a bit of imagination, the Hungries can become infinite containers of anything–tangible or intangible–children can think of.
The Hungries are clearly imagination-dependant creatures as their form factor and character design are fairly simple and restrained. Kids and parents can play together to make the monsters come to life by feeding them other toys and objects, recording messages and storing secrets (whispered to their ears or otherwise.)
All things considered, through creative play and emotional attachment, the Hungries end up containing not just increasingly smaller Hungries inside but also, in a meaningful way, the boy or girl they are playing with (not literally, mind you) and the other way round, recursively.