Yes- they are birds raised to be butchered and eaten and are not suitable for use as laying birds. There are certain management techniques that can be employed to lengthen their life and take them beyond the usual age of processing, but those must be employed from the beginning and that was not...
Cornish Rocks are a meat bird - they are bred to mature and put on heavy amounts of meat rapidly, making them ready to be processed at a very early age. Hopefully this was a matter of mismarking on the box as it does not sound like you are going into this venture wanting to have birds that need...
Congrats on the new additions. If you take and post some photos of your birds here https://www.backyardchickens.com/f/15/what-breed-or-gender-is-this we can help you identify what you have. You'll also want to stop by the learning center here...