One of the best ways to keep children who are deaf or hard of hearing learning during the summer is a language experience book.   This is a time-honored tradition in deaf education classes, and is also used by English as a Second Language teachers, speech language pathologists, and more.   But it is easily adapted for families.  
Here is a link with pictures that is geared for toddlers, but the pictures and the stories are the best visual explanation of this “tool.”  For a language experience book with deaf or hard of hearing kids, I would first take pictures during an event/experience that the child (or student) and I are doing together.  After the event was finished, I would print the pictures and ask the child to tell me what happened (if the child is talking/signing – if not, then do it as the link above describes.)  Even a few words about a picture can be made into a sentence. Then the adult writes the sentence(s) and helps the child to glue the sentences to the pictures, or glue the picture and sentence to another sheet of paper. They can be kept in an inexpensive photo book, in a 3 ring binder, or even stapled together.  Then the child can look back through the book, practice reading about the events, use the pictures to tell another adult about the experience, etc. 
My daughters and I go get ice-cream.  I take a picture of the difference types of ice-cream.  I take a picture of one of the girls ordering their favorite flavor.  I take a picture of them eating their cones (and maybe a picture of Mommy, too!) and I will take a picture of the napkins with ice-cream drippings for “Now the ice-cream is all gone!” 
I may have 4-5 pictures.  I’ll ask my daughter to tell me about the first picture.  Maybe she says “I got lots of ice-cream.” I’ll say, “Right!  There are many different kinds of ice-cream.” and write it down.  Next picture-ordering. My daughter says, “Sissy getting ice-cream.”  I might say, “Sissy is ordering chocolate ice-cream. Yum!”   When we do all of that, I’m going to get my youngest to help paste the pictures and sentences on 8 1/2 x 11 paper and then put them in plastic sleeves and in a big leftover 3-ring binder.