SoCal Waterparks

We've been to 3 of the four you've listed. All have a "Lazy River" type of ride suitable for a 4 year old. I think that Raging Waters has the best play area for a preschool age child. Knotts Soak City has a medium sized area with 2 slides. I would avoid Hurricane Harbor because it has huge lines and seems to be for older kids. Have fun!

Just visited Raging Waters with my 13 yr old son AND 2 1/2 yr old daughter - talk about an age gap in what's considered "fun"! lol

While my son went on "older kid" rides (with his Auntie & friends), I got a place on "the beach" with my toddler. Bring an umbrella as, due to windy conditions, they only accept ones that clip onto your chair or "golf" umbrellas that you hold - NOT one's that stake in the ground - they will make you take them down.

My girl & I had a marvelous time walking through the water (calf deep to to a toddler), going down little kid water slides, standing at the edge of the wave pool, and enjoying the "Lazy River" (with a FREE lifevest provided).

Things to keep in mind if you're on a budget :
1) NO outside food or drink allowed - so pack some sandwiches/chips/drinks & keep in a cooler w/ice in the car. They will stamp your hand when you leave to take your lunch break.
2) Purchase your tickets online - better deals! I bought a family 4 pack (available online only) for $99 & split it w/my friend & her 2 kids...came out to $25 a piece, as apposed to $35+ @ the door. Also, if you plan to go A LOT, consider a season pass - but be aware that the "season" ends in late August (if I remember correctly) might not be worth it for you at this time....
3) If you get there early enough (ie: RIGHT when they open @ 10am), you won't need to spend $50+ dollars on a cabana , although they are SOOOO nice to have! lol You will be able to claim a spot somewhere...just make sure you are there - in line - by at least 9:30am.
4) WORTH IT to spend the $10 on a small locker for your wallet/cell phone...since you will be away from your spot w/your child - and it can get very crowded - better to only leave things you wouldn't mind finding "missing" when you get back (ie : towel/sunblock). Not that I had any problem with that, it's just that I am in law enforcement, so I always think about that kind of thing. lol I only brought $20 (after buying my tix online & packing plenty of food/drinks in a cooler) to splurge on a falafel w/ice cream & toppings.

Hope this helps you, mama! :-)

did you already find your park? we LOVE soak city. i have two sons, 5 and 7, and for both of their preschool graduations the class trip was to soak city. lots of rides are off limits to short kids--but there is so much that is GREAT! plus a special section for really little kids. my kids love it more than disney land. and i think i may, too. wear sun block and get a cabana!!!

What about splash in La Mirada? Never been but the website makes it look nice.