TL;DR Researchers trained ravens to exchange some tokens for food. Presented with a choice of 15 different objects, majority of the birds picked the food tokens and stashed them for up to 17 hours until an opportunity for exchange came again. The author believes this passes as the pinnacle of a 4 year old's planning abilities.
I'm kind of used to New Scientist misreporting my own and others research. If someone has a link to the original study I'd be interested in taking a look. Overall, is it really useful to compare Ravens and human children for their long term planning ability? Human children are still under the care of their parents. There's no real pressure on them to store food tokens...
A raven's memories are for the future
http://science.sciencemag.org/content/357/6347/126
When searching, I also found this, which I missed the first time around, and it might be interesting to some:
Subadult ravens generally don't transfer valuable tokens to conspecifics when there is nothing to gain for themselves