Look into "stair barrier" baby gates. They are very sturdy material with clips on the end meant to be a barrier to interior stairs with two posts at the bottom. Although they are meant for interior use they might work for your exterior stairs (measure your opening to see). I found them on Amazon: https://smile.amazon.com/Stair-Barrier-Baby-Pet-Gate/dp/B07NDMDQJM/ref=sr_1_2_sspa?keywords=stair%2Bbarrier&qid=1560364489&s=gateway&sr=8-2-spons&th=1

What about something like this...https://www.walmart.com/ip/Summer-Infant-6-Wide-Extra-Tall-Walk-Thru-Metal-Expansion-Gate/29505776?wmlspartner=wlpa&selectedSellerId=0&adid=22222222227022152618&wl0=&wl1=g&wl2=c&wl3=40340678672&wl4=aud-566049426705:pla-78298217912&wl5=9017849&wl6=&wl7=&wl8=&wl9=pla&wl10=8175035&wl11=online&wl12=29505776&wl13=&veh=sem&gclid=Cj0KCQjwxYLoBRCxARIsAEf16-ssrYQZtTD_wFhGpb8_cui-0TGFfY_JFD3BL_zqCqtMi39Bz6WI7tkaAjf-EALw_wcB

I would assume you just want a temporary solution. If not then I would look into a contractor or fencer who can do a custom gate.

I would put another section up of the railing using half the width, then finish off the width with a gate that you can secure. We replaced an old wrought iron railing on our front porch with ones similar to yours, and the pieces were purchased at a home center box store. You can mount the sections on the white slab and they may be a couple of inches lower than what is up, but I don't think it will be a detraction.

We can custom make a double hinged gate that would solve your problem. Posts would bolt into the concrete on both sides with a locking hatch in the center. Thank you!

It’s a very temporary problem that doesn’t need a permanent solution. More intense supervision for the maybe year’s time that it will take to have the kid grow out of the fascination will be all you need.

A fall down concrete steps is no joke for a very small child.

Just drag any kind of obstacle in front of the stairs that would take the kid a few moments to attempt climbing over it. A bench or something. This is an area where the kid is going to be closely supervised anyways. It isn't an enclosed backyard. You can see the road in the background.

You just need something that will slow them down so that you can grab them before they tumble.

As mentioned above, it's a very temporary situation for a short period of time. Don't do anything permanent or expensive.

Is your toddler a girl.or boy? Standard baby gate was fine for my daughters but our son was a gate crasher. I would get a real gate like the ones around hotel pools. so you can open it but it would be hard for a little one.