Get a step stool.
If you have a child between the ages of 2 and 7 you need a step stool. Get one that is grippy on the top surface as well as the contacts with the floor so neither the stool, nor the child, will slip. I like Ikea’s Forsiktig Children’s Stool. As your child grows out of the baby stage he will want to do things himself. Having a stool around the house will ease both his and your frustrations immensely. Whenever he is having trouble reaching something, (ie: door handle) ask him: “Where is your stool?” Don’t open the door or reach the object for him. Help him to solve his dilemma on his own.