Rec league soccer is kicking my ass (literally)

Decided to join a parent-kid soccer league with my 6yo because I thought it'd be fun bonding time. Turns out I'm the oldest dad out here and my knees are NOT happy about it. We've had 2 practices and I'm already sore. How are y'all staying in shape for this stuff? Do I just embrace the pain or should I be doing some pre-game stretching routine?