My ds (5 at the end of Aug) sounds like he is on a similar level. We have actually been using the My Pals Are Here science books since the beginning of this year -- I know they are labeled for 3rd grade and up, and I have to read the instructions/write in the answers for many of the activities, but he likes it better. They introduce things briefly, which at this age is good because he feels a sense of accomplishment at having learned something new, but it didn't take a lot of time. :) If he is interested in the subject, we can check out library books to supplement. At this age it is more about doing what his sisters are doing (i.e., his own workbooks) than it is about an actual program. For what it's worth, we had the EB science workbooks/texts from when my dd was younger, but he just didn't like those much. (My dd didn't like them when she did them, either.) He likes MPH, though.
Good luck!