This is a situation where the food forest idea may not be the right idea.
While these work great in private settings, once you try to apply it to public space, where children of all ages will most likely be present,
you run into safety issues as mentioned by Steve Taylor.
Now if you can make certain that the powers that be understand the concept and that the forest will be providing good, healthful food to the park visitors, then you just need to get the community involved with maintenance so it will thrive.
You may find the council receptive and willing or you may find that a longer term approach to the food forest end goal is needed for them to approve the idea.
Good luck, if you can present the council with a landscape drawing so they can see what it would look like once planted, that is usually a great selling device.
Lots of city councils are approving community gardens, where those who benefit also do the work of planting and maintenance.
A plan that shows a food forest operating the same way
should get lots of applause.