Adorable Foster Kittens Play Fighting

I fostered these 3 adorable kittens and their mom from a local cat rescue. The playing and fighting kittens are around 8 weeks old. Almost all of them were adopted into wonderful forever homes. Sadly the white and tabby coloured kitten I named Birch was put to sleep he had had these bursts of energy but would then fall into an intensely lethargic state. Xray showed he had blood in his stomach along with a mass that the vet said was either tumour or cancer. He was most likely born with it and far too youn