Try googling pet gates. The new ones are very attractive and come in all different sizes. All different price points also. $-$$$$$

a downside of pet gates is your child could well learn to open the latch before they are old enough to not need the gate.

dogs don't have thumbs...and 2 year olds are very very clever.

My pet gates are a challenge for all the grown-ups who come to my house!

Depending upon what the top of your staircase looks like, consider a half of an actual door -- the bottom part of a half/half door such as is often used between a kitchen and mudroom. You could then put the lock on the stair side of the half door so a toddler couldn't even reach it.

My friends have a wide staircase and ultimately had to hire a carpenter to build and install a custom gate. the way their home is laid out there just wasn't any way around it.

I have a wrought iron staircase and hired a contractor to custom-make me a wrought iron gate at the bottom of my staircase. It's been highly effective with 3 boys and even stops my dogs from visiting our house guests in the middle of the night (guest room is upstairs). The gate is so pretty and I am surprised at how many compliments i get on it; it doesn't look like a baby gate at all. Well worth every penny and I'll leave it on even when my boys are grown.