please take a look at this site, it will give you details at to what can be sent and what not to send. and how they can get in trouble.
Do not send musical or recordable cards, or cards/letters with glitter or flocking that comes off, or contains confetti, or anything that will be messy or draw undo attention to your recruit. (Glitter and confetti are difficult to clean up and even one speck would be considered "gear adrift" and result in a "hit" on an inspection.) Some RDC’s do not permit newspaper or magazine clippings and others do. (One reason that RDC' s do not permit newspaper or magazine clippings is that the ink may transfer to your recruit's hands and then to clothing and/or objects within the compartment.) If you want to send articles (such as information on your recruit's favorite sports team), then copy the information either on the computer or a copy machine and then write your letter around it by hand or on the computer. Printing or writing your letter on both sides of the paper will reduce the number of pages. Write about anything and everything except things that will distress your recruit. It’s fine to let your recruit know that you miss him/her, but always follow it with how proud you are of him/her and how much you are looking forward to seeing him/her in his/her dress whites or dress blues at PIR as a US Navy Sailor
The group, Letter-Writing Navy Moms also has suggestions for things to write.
Sending cards and letters in colored envelopes does not usually cause a problem for the recruits. Some (not all) RDC’s will give IT (Intensive Training—extra exercises) for colored envelopes and stickers on the outside of envelopes and others don’t care. If the division or your recruit needs extra help to be ready for the PFA, then the RDC is going to look for every opportunity to give IT so that everyone makes it to PIR. If your recruit indicates that you should write in a particular color of ink or tells you not to send something, then pay attention and let others who are writing him/her (and those in your PIR group as well) know. Do avoid using red ink when you write; there is a red light on at night and if your recruit decides to read a letter before going to sleep (even though they aren’t supposed to), s/he will have difficulty reading red ink. You want to avoid sending anything that will require extra postage because that is a red flag and your recruit may have to open the letter/card in front of the RDC. If you have more than 4 pages in your letter, have a postal clerk weigh the envelope. *If you will be sending lots of pages (such as when a class writes to a recruit/division), have a postal clerk help you determine the maximum number of pages you can send using the paper and envelope you plan to use. One ounce goes for the standard postage rate, so you may be able to send more pages with a lower quality of paper than if you use a high quality paper. What happens after the recruit opens mail in front of the RDC all depends on the RDC and his/her mood at the time and how well the recruit/division is doing at the time. Although post cards are permitted and will save you postage, be aware that post cards are often read aloud, so some put post cards in an envelope and treat them as a greeting card instead.
I was told to use only white standard envelopes, but lots of people send cards or use colored envelopes. Glitter is a no-no. Here is a link that might help. http://navyformoms.ning.com/group/bootcampmoms/page/letter-writing-...