Can you give me more information about the symptoms that you are experiencing as well as the specs of your rig. Concerning the theme well when the panda eat bamboo it grow, the more it eat the more it grow (stop eating and it shrink over time). A bigger panda make it easier to reach higher ground, beat the baddies allows it to push crates etc... but makes it harder to avoid traps, stay on moving platforms etc.. you get the idea ;)
Thank you for saying that it look polished, we made a few tutorials in the past using Kenney assets so we already had a head start check it out:
NRG - Micro Games (nrgcore.com)