1. Malay Idiom Dictionary from Bahasa Malaysia Simple Fun dot com - Living in Malaysia, you have to know some Bahasa Malaysia. However, if your BM is not as good as it should be, this site will be very useful for you to help you explain simpulan bahasa to your child because it is explained in English. However, the list appears to be stopped at K. Also, this site is more for adult learners of BM so the list tends to be geared that way. Still it is a very good resource because it is not easy to find a bilingual one.
2. Simpulan Bahasa from Peribahasa SPM blogspot - I like this one because it is comprehensive. I could find most of the simpulan bahasa definition I was looking for. Maybe because my kids are in primary school but this one is for SPM so I could easily find most of those that I was looking for, even the not so common ones. This is fully Malay. If your Malay is not so good, you can always use Google translate to help you with the meaning.
3. Wiktionary: Simpulan Bahasa - Since this is an open dictionary (A Wikikamus or Kamus Bebas), you will naturally be able to find a good simpulan bahasa list given in alphabetical order. If you ever need to look up the meaning of a simpulan bahasa you do not know, try this wiktionary of simpulan bahasa.
4. Kamus Simpulan Bahasa from Slideshare - a slideshare user has downloaded an entire kamus simpulan bahasa for sharing. You can check it out here. More suitable for primary school usage.
5. Kamus Simpulan Bahasa & Peribahasa App from Google Play Store - If you have an android device, then you can make use of this simpulan bahasa dictionary. Just install it on your device and use it to search for the simpulan bahasa you want.