This criminal history information could possibly show up on a background check performed by your grandson's school district. You need to contact the Clerk of Court in the county(s) in Maryland where you had these priors and determine what the outcome or disposition was. Their records might also be on-line too. If you are eligible under Maryland law to seal or expunge one of them, you can go that route as well. Given the age of these priors and depending on what they were, you may not be denied access to the classroom as a helper. You just need to have all the relevant information to be able to provide it to the school to establish you are not a danger to the students in any way. Good luck.
No one can stop your prior history from appearing on a criminal background check. You are free to try to seal or expunge your old MD cases but, I am certain that once you do so they will be "red-flagged" and then they will certainly be gobbled up into various private internet data bases that intentionally store such information so as to be able to extort good folks like you into paying them to remove it. Sadly this is a lawful practice (its one of the side-effects of technology and being in the internet age).
My advise is to be honest and upfront with the school. 20 year old out of State misdemeanors, standing alone, by a grandma (assuming that you are a normal sweet kind grandma and not a Honey-Boo-Boo grandma), should not preclude your good intentions, but, sadly, I cannot guarantee you that either.
I can tell you that if you fail to disclose and they find out on their own, especially after the fact, you will likely be banned from the school (and they can do that too). Honesty is your best policy in this situation, and the good news is that this won't cost you any legal fees!
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