Don't be alarmed. They are just grain beetles. The larvae is sometimes packaged in the box and when they reach the right conditions, they hatch.
Be thankful that they hatched or you would have, and probably have in the past, eaten the larvae.
You can get them in macaroni, flour, etc. If you want to avoid seeing them "after the fact" put all your grain products in clear glass jars so you can monitor them.
If they are crawling around your cabinets by now, just vacuum them thoroughly and throw out the bag.
How do I know this stuff....I've been an exterminator for 35 years.