Great question! I don't know that I have the answer, but here is our situation and what we did about it....
We don't have little people, but we have two little Pomeranians. The PC screen door has a latch which is 'spring loaded' on the door itself. This latch comes in a variety of tensions from the manufacturer (Southco Inc) and I don't know what the standard tension is on the PC. Here is what it looks like: http://www.amazon.com/Southco-SC-4320-Side-Mount-Grabber-Catches/dp/B002I05TUQ/ref=pd_sim_sbs_hi_2
Now, the PC's have a step down before the screen door. Our dogs love to look out the door, sometimes jumping down into this step-well and right in front of the screen. Since the door is latched mechanically with a spring tension, if they jump onto the screen it might unlatch and spring open.
There are probably dozens of solutions, but I can give you a couple. For us, we installed a manual 'lock' to ensure the screen doesn't flip open with force from a four legged creature. I am attaching pictures, but they may be 45 degrees rotated for some reason...have to figure this out. The installation was extremely inexpensive and very easy to install. It has worked out very well for us and we don't worry about the dogs nearly as much if we wander a bit from the rig.
Another solution.....friends of ours have a PC3100. They also have dogs. They are installing a 'hinged', removable three-sided barrier which fits into that step-well and comes up about 2 ft on three sides to keep pets out of the step-well and away from the door.
The screen door is very neat, in that it slides out of view when not in use and easily closes when you need it. Unfortunately, it has no 'lock'.....and I haven't even found anything that I could retrofit from other patio type screen doors.
Hope this helps a bit...