My son is 3 years old and weighs 32 pounds. I found a booster seat that says it can be used at 30 pounds. Is this a good choice for an extra seat in Grandma's car? His main seat is an Evenflo Chase in my car.
No. Your son is way too young and too light to use a booster seat. The minimum for booster use should be 4 years and 40 pounds. A child less than 40 pounds doesn't fill out the seatbelt well and can submarine (slip under the seatbelt) in a crash.
My daughter is 3 1/2 and weighs 38 pounds. She needs a new seat as her only goes to 40 pounds. Is the Highback Graco Turbobooster a good seat?
Yes, that is a nice booster, but not for your daughter. At only 3 years old, she too young for a booster and should remain in a harness. The minimum for booster use is 4 years and 40 pounds. However, many children aren't mature enough to sit properly the entire ride until 5-7 years old. I would suggest the Graco Nautilus, Safety First Apex 65 (If your vehicle has headrests), or the Britax Frontier. They will all keep your daughter in a harness longer (up to 65, or 80 pounds). They can also convert to a booster once she's old enough.
Here are some videos on children that were too small for the booster seats they used.
Another for Isabelle http://www.youtube.com/watch?v=KPBSEQ4xbTw&feature=related
Kyle's family on Good Morning America http://www.youtube.com/watch?v=9pDnBO76RFM&feature=related
Those videos are not saying booster seats are bad, or that your child needs to be in a harness forever. They're simplying showing you what can happen if a child is too young/small for a booster; even if they meet the minimum requirements on the seat.
If you want to support a group that donates high weight harness seats to families that can't afford them, please visit the Kyle David Miller Foundation http://www.kyledavidmiller.org