Best advice I've received for toddlers being mischievous was from my mom, who raised her own kids and also taught preschool for many years: Don't talk across the room for them to stop doing something and not follow through. Always follow through. As days go by, they may do something naughty over and over (grab something off the counter, come out of their room when it's bedtime, get out of their chair at dinner, etc.), but all you have to do is do it one more time than them. I've also heard it called "GOYA parenting" (get off your ass parenting). Say it once: "Little Susie, don't touch that vase please." If Little Susie doesn't do it (which she probably won't), physically get up, go over, and stop her hands. It's frustrating because you have to do this with so many things, so many times, but in my experience and my mom's, it's the only way to teach them you mean what you say and are 100% ready to carry it out. Then, and only then, will they start believing your commands as they get older. I'd just advise starting as soon as you can when they're small. Because when they're 60 lbs. at 7yo and you tell them it's time to leave the playground and they won't, it's a lot harder to go over and physically carry them to the car.