It's one of the biggest parenting challenges: getting your kids to go to sleep, but it's so important for their developing brains and bodies. Sleep recommendations vary by age, so here's a handy reference chart.
The chart was posted by Wilson Elementary School of Kenosha, WI. There are some typos in the chart (see age 8 waking up at 6am) and other oddities, like some sleeping times not going up in 15-minute increments for the kids ages 8 and under, but you can consider these just ballpark recommendations that are a little more specific than the broader 10-13 or 9-11 hours recommendation from the US National Sleep Foundation.
If anything, you can print out the chart and post it somewhere prominent with the bedtime highlighted as an "official" reminder that, kid, this is your bedtime and you gotta go to sleep.