Here are some of the suggestions:

1) Magic Treehouse series

This is a very common series that talks about 2 children who go back in time to interesting events that happen in the past. For example: the volcanic eruption in Pompeii and how they try to solve some puzzle there or help someone during their travels.

2) Tremors

This series is very interesting. There are not many words so a reluctant
reader will find it easy to read and yet the plot is interesting. Sometimes
books that are thin have boring and simple plots so this series is good.
However, one warning- the stories can be a little eerie.

One story is about a boy who wakes up and finds that he is back in the past and he has to help a great grand uncle or some distant relative survive a storm. Some stories are on ponds/camps that are haunted but the ghost is not really scary. The stories always have a twist in them as well.
Most children are not scared when they read them but if your child has an active imagination, he might be. So it would be good to look through the books first. The words used are also good. (there are quite good descriptive phrases in them)

3) Magic Mischief by Anna Dale

The shop owner encounters a stench in his shop that somehow turns to magic and his shop becomes the breeding ground of much magical mischief (thus the title)

4) Destined to live by Ruth Gruener

This true story is about a girl who survives the Holocaust. It talks about how her world turns upside down when the Germans invade her town and how she has to flee for her life. She later settles down in America and has to adapt to the culture there.

It is a good book to introduce your child to history and to some of the atrocities that happened and to also share with your child on racism.

5) 39 clues

It is a series of books that follow 2 children as they travel from country to country to try to retrieve some clues to piece together a puzzle that their deceased aunt left for them. However there are many others on that same hunt and the other parties try to sabotage their hunt. It is something like a book version of ‘Amazing Race’ but a bit more deadly one. Interesting!