Haha! m3gmi dear ... hi!
First thing first ......:
The people of Malaysia would like to greet you and your love ones,
"SELAMAT DATANG TO MALAYSIA ! "
We welcome you and hope you have a pleasant & memorable stay here.
I'm not sure when summer school holidays starts in Japanese schools or international schools, but in general during school holidays for Malaysian kids ... they would be pretty much engrossed with extra-classes on school subjects or tuitions to do some catch-ups, as most of their parents would want it that way ~ although not all of them.
Some will attend to camps, outward bound school, additional music lessons or seek improvement or upgrade on their English language verbal/written skills through specialty centres.
During my time, my parents would send my sister, my brother and me back to our hometown (kampung) to spend time with my grandparents. It can be a lovely experience though as we got to experience "city life" .... and the easy-cosy "kampong lives".
Perhaps on your end, you may try:
A. On weekdays while you are at work
1) some homestay experience (select ones that are reliable, not too far away or good through recommendations or by just google to check it out) for them;
2) to send them to learn a specialty skill like ones of Morris Allen, or a Tennis clinic like Monster Tennis/Duta Tennis or to pick up a skill on climbing like Camp5 or simply to improve on their water confidence skill like swimming or a certification on Junior SCUBA/Introductory SCUBA and etc. Or you may let them to try out the KidZania at the Curve! It is an interactive edutainment centre where children can experience the world of adults in a replica of a real city. I think this can be interesting to you. Please google if possible...
B. On weekends where you can be with them
3) having a day-trip out from Kuala Lumpur to places such as Malacca or Ipoh (you may need to start really early in the morning as it can take the whole day. Both have pretty good food there and for sightseeing), Tanjung Sepat (famous for fish balls, lime honey juice in a bottle, Pau/dumplings etc.), Kuala Selangor (famous for crabs/seafood, fresh sea produces from fishermen, coastal kind of drive by explore/experience small town lifestyle),
Note if you have more than a day, say 3 days or so, the I would suggest a visit to Penang Island, Redang Island, Tioman Island or any other East coast island but do make sure that you have accommodations booked in advance. If you do not like beaches or being tanned, then possibly a visit to LEGOLAND or Angry Birds Activity Park or Putri Harbour Family Theme Park (1st Sanrio Hello KittyTown outside of Japan) at Nusajaya, in the Johor state (southern part of Malaysia peninsular.
4) having a day out within Kuala Lumpur (Klang Valley surroundings) such as visits to Zoo Negara (Giant Pandas/aquarium), Aquaria KLCC, try the Skytrek Adventure Park out, I-City in Shah Alam, go to a water theme Park like the Sunway Lagoon or others and with a good buffet dinner to wrap up for the day or if you love nature then, FRIM (Forest Research Institute Malaysia) is recommended as it has a waterfall inside, some hiking possibilities and some mountain-biking course as well. Bandar Utama has got plenty of kids stuff too such as "It's A Hit! Batting Cage" if baseball is what it is all about, then there's ice skating facility inside Sunway Pyramid shopping mall and the list goes on.
There's plenty of other activities going on as well in Kuala Lumpur/Subang Jaya/Petaling Jaya area which I might not be aware of. Again, this all depends on the kid/kids' age ... and also to your consensus. Hahaha!
Wish you good luck and hope you will get to find some really interesting program during that time.
You are welcome to write to me if you want, anytime.
Ganbaruzo!
warmest regards,