Keeping your young child safe is a full time job, especially if you have a stairway. You think you are watching your child closely, then you turn around and they are at the head of the stairs ready to fall down. What you need is a baby gate. If your stairway is effectively blocked off you have no worries about your child getting near it. Not only can you block the stairway, but you can also use baby gates to seal off any room that you don't want your child to have access too. Its a measure of safety that you simply can't provide with vigilance.
Baby gates are an essential item to keeping your child safe, but the same product is handy for pets. Pet gates can be used to block your pets from any room in the house, or to simply keep them confined to one room while you are at work. I used one here in our home when we had inside pets. We had dogs that were house broken, unless we were gone, and then they would pout and do what they could to make sure that we understood their displeasure at being left alone. We used pet gates to confine them to a room with an uncarpeted floor, and then if they made a mess it was easy to clean up.
Baby gates and pet gates are easy to use and provide an extra measure of safety for your child and pets. When it comes to children and stairways, sometimes you don't get a second chance. Better safe than sorry.