Recommended Summer Workbooks
Almost every year I get my kids the Summer Bridge workbooks to help them retain all their knowledge over the summer. It is a simple worksheet or two a day, and it is full of fun ideas like science experiments, fitness ideas, and it includes a rewards chart. The workbook covers the four major subjects: math, reading, writing, and language arts. It also offers a list of recommended summer reading books, and since they update these books every year they are usually popular books my kids knew. Summer Bridges has workbooks for every grade level.
If you child struggles with creative writing then Unjournaling is a must for the summer. The topics are both funny and puzzling, but also a lot of fun. We got this for my son one year, and it became a family game to do our own as well. My son was actually disappointed when he finished it. I can't remember any of the topics specifically, but it has stuff like: Write a sentence about a mythical creature where the first letter of each word is in alphabetical order. As you see it is a bit challenging, so I would recommend it for older children who can read and write unassisted.
Hot Fudge Monday is a great book if your child is struggling with parts of speech. The book is broken into chapters which focus on a specific part of speech, such as adverb. It walks them through gently on what it is, how to identify them, and how to work out the tricky sentences that are more challenging to identify the proper part of speech. This book is a bit challenging at times, so I recommend it again for older children or a dedicated parent who is willing to sit down with their child.