I'm from Sacramento. Just did the drive from Sacramento down I-5 to San Luis Obispo last week and I agree, I-5 is BORING!!!!! 99 may be slower but it's like a wonderland compared to I-5. Both are two-lane roads but there are few stops on 5 - one big rest stop and not many gas stops at all. 99 has many bathroom stops as well as eating places and just things to look at...cities, towns, signs, etc. More opportunities to play the "ABC Game", haha...not that you could do that all day!
I second the PP who mentioned Bravo Farms off of 99. I've never stopped there myself but it looks interesting and would break up your drive. If you're into a slightly longer stop, Visalia (off 99) is a kind of cool town with a nice little downtown and restaurants too.
I prefer flying to D-land but if I can't, it's all about driving fast with minimal stops. I'd load up on the car entertainment...maybe do little surprise treats for the day of, or pull out something new every couple hours? Talking and interacting actually made our last drive from D-land (last fall) go surprisingly quickly, but then again, we're adults. I don't have great advice for little kids, sorry!
Edit: I was on Hwy 46 last week (from Sac to SLO) and it was fine. I didn't see where in N. Cal you're from, but it really seems like going that far west of I-5 would add a ton of drive time. Maybe that's ok with you if you're in search of scenery but really, to get scenery you have to be way out by the coast down in that area. If you want to avoid 5, I'd say take 99 more of the way, but otherwise just stick to 5...tough it out...that's my advice. ***Do avoid Hwys 269 and 33 near Avenal, if you decide to cut west of 5 and think that's a "shortcut". They're doing construction and we were delayed about 15 minutes, just sitting still in nowheresville.