So sorry you were let go of a position you really liked as I am sure you were good at what you were doing for them.
Much depends on why you were let go of the position. If it was because of layoffs, then I would agree that setting up a meeting with your old boss to see if there is someway to become employed again, maybe part-time to start.
If you were let go because of a problem that made your old boss fire you, then also consider talking with him or her and explain what went wrong and you hope that another chance can be offered. No guarantee that the old boss will hire you back but if you show that you are sincere and want to make things right again, then asking for a meeting would be a good idea.
Before going into any meeting, sit down and review what you want to say as explaining this to the boss. Explain how things went not as well as you hoped but want to make things better this time. Offer to work any hours asked as well as any position that is open that you can start with.
Wishing you the best of luck in setting up the meeting. Please let me know of any additional questions and/or concerns you may have. Also when done with the question that if you could take a moment to rate my assistance so that I can receive credit for assisting you this morning.