My daughter and I invented the ParentSaddle Child Carrier around 2008 and patented it: US Patent no. 8,474,667.
You can make one yourself as you see in Figure 1, even just a strap will do, but the foot can slip out, and it can hurt the foot, so you might use some padding as in some of the other figures above. It may be better to use something a little elastic for the "around the chest strap" because then it can be pretty snug on the parent, but still allow you to take deep breaths. Then you can find a way to connect the child's foot into the strap.
This fits in your pocket and just allows hands-free walking, or running... or biking (OK, I've tried it once and no one died, but I really don't advocate riding a bicycle with a child strapped onto your shoulders.) It's amazing what kind of freedom you have running around with a child strapped to you, as shown in this video with me running around with my daughter: ParentSaddle in Action. You can't do this kind of activity with other carriers because they are bulky and don't let the child completely connect to you.
If you make one, keep in mind that if your child falls out, they can land on their head and get hurt or die - I'm sure you know that, right?
I met someone who can produce these, but we need someone to manage the marketing and sales. If you're interested, contact me at email@example.com.
While you're of course welcome to make one for yourself, I retain the patent rights for commercial production.
No, we didn't make this at the SLO MakerSpace in San Luis Obispo because it didn't exist in 2008. However, it's a good bet that if it had, I'd have wanted to create it there!