That's up to you, but you should stop using the high chair when your toddler can crawl out. At that point, move to a booster or child seat. Some kids can climb quite early so use your best judgment. Also, when your child can repeatedly unbuckle the harness unassisted, they are ready for a more grown-up seating option like a booster. The booster is just to help them reach the table as they are short.