Screen time battles every single day - any tips that actually work?

My kids would literally stare at screens 24/7 if I let them. We set limits, we use parental controls, but it's constant fighting. They ask for 5 more minutes, sneak devices when I'm not looking, get angry when I take phones away. I feel like a bad guy but I also see how different they are when they've been glued to a screen all day. Does it get easier as they get older or am I doing something wrong with the boundaries?