Runts often catch up, or develop normally after a rocky start but behind their siblings – so eyes open later, fur grows in later, they look younger – but they tend to be perfectly healthy and happy. I don’t give runts any special extra feeding or attention, I feel that if they make it, they’ll make it. If they don’t – then maybe there was something more wrong with them than just the bad luck of a poor position in the womb. Obviously if a young kitten looked to be suffering, then it should be humanely euthanised.