How much warm-up do eight-year-olds actually need before a game?

Twenty minutes would be more than I need with most U8 groups. I want them physically ready, familiar with the ball and mentally engaged, but I do not need a miniature training session before a 40-minute maximum game. For this age I’d keep it simple: arrive, get moving, plenty of touches, a short game or 1v1/2v2 activity, maybe a few finishes, then play. The best warm-up is often something they enjoy enough that they do not realise you are “warming up”. I would also look at what the children are like at kick-off. If they are already flat or asking for a drink, the warm-up has probably taken too much out of them. There is nothing wrong with structure, but the purpose should be readiness rather than proving how organised the coach is. Ten active minutes can be far more useful than twenty minutes of lines, stretches and instructions.