NO CHILD SHOULD RIDE IN A BELT POSITIONING BOOSTER UNTIL *AT LEAST* AFTER AGE 4! There is a difference between a belted booster and a harnessed booster. Harnessed boosters are called Combination seats, meaning they have a five point harness to 40lbs, and then the harness can then be removed and used as a belted booster. Belted boosters have NO HARNESS AND SHOULD NOT BE USED FOR CHILDREN UNDER AT LEAST AGE 4.
Children are not mature enough to ride in a belted booster until AT LEAST age 4, car seatbelts are NOT MADE FOR CHiLDREN! and its so much safer to keep them in a 5 point harness until 5 or 6. Britax makes wonderful seats that harness up to 65lbs, and even 80lbs. Sunshine kids Radian makes a harnessed seat up to 65lbs, and the Cosco Apex also harnesses up to 65lbs. Britax runs around $250, Radian around $200, and the Apex around $150. All of them are great seats. The Apex requires headrests on your car seats, or you can't use it. Radian is an all metal seat so its very heavy if you plan on moving it from car to car. Britax is the easiest to find, use, and they are great seats. So if your child outgrow his/her current seat before he/she is 4 years old, consider one of these seats so you can keep him/her harnessed longer. Its PROVEN that five point harnesses are safer for children than regular seat belts, and even belted booster seats.
Your one year old would still be safest rear facing in a five point harness until he/she outgrows the rear facing weight limit, and should remain in a five point harness until at least age 5 or 6.
Your two year old needs to be in a five point harness agian until AT LEAST age 5 or 6. You would be putting your child in great danger by putting her in a belted booster before age 4. She simply wouldn't be big enough, or mature enough, and though sometimes carseats can be very controversial, there is a reason these seats are now having higher weight limits. Its because everyone now KNOWS how dangerous a regular adult seatbelt is to a child under the age of 6.
Also carseats EXPIRE after 6 years, so everyone reading this please check the expiration date on your carseats. They are no longer good after 6 years. If you have an expired seat, please cut the straps, remove the cover, and throw it away. And don't be fooled by seats that claim 'you'll never need another carseat' because in all reality your child will probably outgrow a 40lb weight limit seat in HEIGHT much before WEIGHT. And it will expire in 6 years, your child needs to be in a seat until at least age 8. And a child under 40lbs and under age 4 minimum needs to be harnessed.
www.carseatsafety.gov is a great site for information on carseats.
Again, please don't even consider a belted booster until your child is AT LEAST 4 years old, AT LEAST 40lbs, and AT LEAST 40 inches tall. Please send me a message if you want any more information on carseats and safety. I'm willing to help anyone with questions.
**ETA yes Jennifer, I do know what I'm talking about. I know the MN law of 4yrs/40lbs, but there is also a reason that other states are CHANGING thier laws, and MN will more htan likely follow soon. There is also talk of requiring other companies to follow the lead of Britax and make ALL seats harness up to 65lbs, and make that the requirement. You can't argue hard core evidence that five point harnesses are safer. So whether you think I'm a know it all or not, my post gave tons of good information for ALL parents.
And to the original poster, I assumed you weren't going to put your two year old into a booster, however some parents reading this might, and since carseat safety is one of my passions, I posted as much information as I could, and made it as helpful as possible, for you and for other parents.