For smaller kids, you can create your own presentations related to their study subjects. Involve them also to make it a wonderful experience. they learn it better too.
For example, for those preprimary kids, ask them to say A for Apple, B for Ball and record them as separate clips and save them as A.wav, B.wav..
Create a powerpoint presentation using related pictures, I used google images and made my kid chose the picture himself. Now keep this picture as back ground for that particular slide. Instead of changing the background option, paste the picture, pull it to the whole slide and "send it to back" and bring the text to front. in the sound settings, choose the appropriate wave clips for each slide.
when you play the slideshow first the picture would appear, then the letters along with your kids voice.
you can create slides for good eating habits, cleanliness etc too.
If anybody want a sample, let me know with your email ID .. I will send that to you..