I haven't actually stayed at either of these places yet, but we are planning a stay at both Umlani and Kambaku in the Timbavati area of Kruger in just a couple of weeks. Both lodges allow children to go on game drives (mine are 5 and 8), and have some activities, games, etc., for children. Additionally, we are not staying there, but Honeyguides also had one camp that allowed children. Thornybush also allows children, but not on the game drives. Instead, they have activities and babysitting during those times.

I don't know what your price point is, but while we found the cost of both camps (Umlani and Kambaku) to be eye-wateringly expensive, they do seem to be significantly cheaper than many of the other options. Of course, you could also just stay in a SANpark rest camp, and drive yourself about, which would be a lot more economical.

(Also, you probably already know about this, but there are paediatric malaria tablets available now, conveniently suitable for ages 4 and up, depending on the size/weight of your 4-yr-old.)