Always add meat to your resume related to whatever you want to be doing at the school you are going to. For instance, if you wanted to get a degree in legal social work (court-appointed social worker, CPS cases, things of that nature), you'd be well on your way. However, if you wanted to go into Substance Addictions Counseling, your resume is severely lacking.
Volunteering is a fantastic option. Again, just make sure you have a focus on what you want to do. If I were looking at a resume that noted all the things you have, I'd be curious as to whether or not you'd ever finish. Not because you don't have the intelligence, but because you seem to have been field-hopping so much.
You've mentioned education or experience in:
Psychology
Human Development
Family Studies
Spanish
Sex and Gender Studies
Environmental Safety
Case Management
Civil Investigation
Human Sexuality
Art Therapy
WHEW!
Compared to a sad little resume like my own which features:
Addictions Counseling
Interpersonal Skills Training
Writing
So, if you plan on actually going to graduate school for something directly related to ADHD (for instance, counseling adults or children with the disorder), then applying to the Johns Hopkins position is great and the homeless shelter position is probably just going to "confuse" your resume further.
As you stated, you have all these short-lived experiences in these different areas, and that may make you a less attractive candidate. You may come off as a jack of all trades (master of none).
Honestly, I'd just sit down for an hour or so somewhere quiet (library, cafe, park, etc.) and really think about what I want to do. What would make me excited to get up and go to work in the morning (on most days)? What is something I would do in my spare time, for free? What talents do I have that I could spread throughout the world and feel good about the work that I'm doing with people?
These types of questions can help you gain a central focus. Once you know exactly what you want to do, every step you take can be geared towards coming closer to that goal.
Hope this was helpful. I'm wishing you the best of luck!!