Don't forget to read with your child over the summer. Find a book that your child can read with a tiny bit of difficulty and take turns reading alternate pages with them. Encourage them to sound out simple words (consonant-vowel-consonant words and four-letter words that end in silent E are all within the capability of students going onto first grade). Help them with any harder words. When it is your turn to read, use expression and voice the characters. Don't be afraid to be silly. It shows your child how to enjoy the book.
Ask your child to recognize numerals between 10 and 20 (most can name them up to 100 or higher). Practice skip counting by 5's 10's, and 2's as you count objects (like nickels and dimes and pairs of shoes). Sort things (toys, books, etc.) by colors or shapes or whatever attribute makes sense to your child.
For incoming kindergarteners, point out letters and see if your child can name any of them. Review colors and shapes in your world. Sing your ABC's, making a point of saying L-M-N-O-P very carefully, separating them so that your child doesn't think it is all one letter. Count things (steps as you climb them, chicken wings in the box, forks as you put them away, etc.) to help your child learn their numbers in order.
For 4, 5, and 6-year-olds, sing nursery rhyme songs (or learn them with your child - many are online), dance together, move together (bike, walk, run, play sports), take your child to movies and parks and museums. Expose them to opportunities to explore and learn about the world. Children with more experiences are almost always better readers, because they have images to connect with the words they read.
Also, check out the list of iPad apps I have added on a new page. I have found so many great ones for free, free to try (then upgrade for a nominal fee if you like them), or for a small fee (mostly $2.99 or less). Your child lives in a digital world, surrounded by phones, tablets, and computers. Use them to add to your child's learning, rather than a distraction.