i have a total of 11, count 'em 11 peircings(i count my lobes as one..though technically i have 12 pierced holes).
i have four peircings in one each, two in the other ear, a double eyebrow(after re-piercing a horizontal eyebrow 5times cuz it kept rejecting, which isn't that uncommon for surface piercings, into scar tissue that had only been left to heal for two weeks each time then gave up on it), my navel, my nose(just got that done), and my breasts done.
as long as you clean them(though i even stopped that process after a month or so honestly), have good hygiene and keep an eye on them for infections(if they start to get really red or hurt, go see the piercer) you SHOULD be fine. that's not saying you will be, but in my experience, i have yet to take a piercing out because it got infected. i have had infected or sad looking piercings before, and all i did was go to the piercer, was told to keep cleaning them, it was just my body trying to fight this foreign metal, and if my blood sugars go outta whack or it gets worse, go to the doc for anti-botics(have yet to have that happen, the cleaning was enough).
when you go, they are gonna ask you to fill out a sheet, so you're gonna have to let them know anyways. won't really mean much, they will just tell you to be extra careful since diabetics are more likely to get infections.
one BIG thing though...do NOT go to a place like Claire's where they use a GUN to pierce you. If you're gonna do this, do it RIGHT and do it sanitary! Go to a tattoo and piercing parlor with your parents and get a professional to do it with a NEEDLE. the guns are DIRTY and the girls who peirce with them are untrained. make sure you go to a place that has a good reputation around town and is clean(your parents might think they are dirty cuz well..my mom did. she was intimated by the parlor until she met the piercer and he joked around with her then i got her to take me when i was 16 to get my navel done.) another good thing about going to a professional parlor, is that they use titanium steel to pierce you..none of this cheap gold and silver crap Claire's and the likes put in. I almost had to give up on my ear piercings because of the crappy jewelry they put in my ear when i was 8. the reason it got infected, could be due to the jewelry, i can't wear anything cheap to this day because if i do..within 15mins my piercing will start to get irritated and red.
if your parents have any questions, you can always get them to e-mail me(natalie[at]nataliewoods.com) and i'd be happy to help ease their concerns! :)