To start constructing this DIY backdrop, measure how thick your elbow is compared to your curtain rod, and add electrical tape around the end of the rod until you have a tight fit. For most people, it will be easier to put a little bit of tape on at a time, testing the fit every so often until it’s snug, but measurements can give you a good base to start with. Don’t attach the rod to the elbow yet, however.
I would definitely play around with it. Your not going to want to go too wide with 4 because odds are they will move around a bit and you’ll end up with some soft faces. Some key things to remember would be try to keep their faces all on the same plane of focus, that will allow you to shoot a little wider. Generally with 4 kids I would aim to shoot around f/4 but certainly play around. At that aperture you may want to consider moving them further away from the background. Keep in mind the closer you are to them and the further away from the background they are the more bokeh you will get!
Having skills in a variety of lighting techniques for your photo backdrop can give you some wonderful options for creating beautiful imagery for either products or portraits. By brushing up on your exposure and composition know-how along with practicing prior to your actual shoot date you’ll quickly be able to build a portfolio showing off your creative depth.
So why only 4 stars and not 5? I personally don't like the very top of the backdrop. If you look at the pictures carefully (I don't know if you can actually see this because I tried to crop these out), it looks like there are ceiling lights on a dark alley street. Scientifically, that's impossible and realistically, it looks WEIRD. But other than that, it's near perfect for what you're paying for.