Hello and welcome!!
When your kitten plays, does he/she breathe funny(mouth open)? Have you noticed any blueness of the mouth?? Does the kitten's heart feel like it is racing(beating very fast)? I am just wondering if the kitten may have something cardiac going on. Years ago, I noticed our then kitten, Riley, while he was chasing a toy, started to pant(breathe thru the mouth), and a bluish tint to his oral area and his heart was racing! I called our vet and made an appointment for a cardiac evaluation( I am a RN besides mother to 8 cats). Our vet heard a Grade III cardiac murmur and upon cardiac ultrasound, Riley was found to have left ventricular hypertrophy. All that means, is the left ventricle of the heart(where the blood is pumped out from to the rest of the body) was enlarged. RIiey was lucky, he has not had symptoms and is not on meds(some cats need a special diet and meds). He will be going shortly for a repeat utrasound. I think it is worth a call to your vet to get kitty checked out. Please let us know what happens!!! Sandra