Capacitor question - energy from pushing a baby stroller
Your question can, I think, be stated thus:


  I want to harvest energy from a baby stroller motor while it is being pushed on the level or downhill and store the energy in a bank of capacitors. On reaching a hill I want to use the stored energy to drive the motor to assist with propelling the stroller.


The normal practice here would be to use the motor as both motor and generator. The voltage you'll get out of the generator at a certain speed will be a bit less than the voltage that will drive the motor at that speed.
For example, if 10 V causes the motor to drive the stroller at 2 m/s then pushing the stroller at 2 m/s might generate about 9 V. It will also act as a brake on the stroller so it will be harder to push.

Next steps:


Turn your motor at the speed you think it will run at in normal walking.
Measure the output voltage.
If you can, apply that voltage to the motor and confirm that it runs close to the same speed as discussed above.
Measure the current drawn. You'll need that to work out how much energy you need to store in the capacitors.
Post the results in your question and we'll go from there.



  My issue is that the capacitors still don’t combine voltages, I have 0.7 volts for all three capacitors, so the 2 volt LED should be turning on in this configuration, but the voltage on the LED is the exact same as the capacitors, 0.7 volts.


Your capacitors are in parallel when you charge them and are in parallel when you're trying to use them so the voltage is still 0.7 V.