A.P.
As the previous poster mentioned, the at-fault insurance company is responsible for reimbursing you for the replacement of those seats. HOWEVER, you have to be vocal about it. It should come out of the property damage settlement, but some insurance companies do not see the seats as permanently attached to the vehicle, so they may refer you to the liability adjuster. You can make the argument that the seats are required by law anytime the children ride in the car. Basically, if the PD adj. doesn't give it to you, make the liability adj. give it to you. If all else fails, you can file it on your homeowner's insurance, but if you are like most people, your deductible is more than the costs.
Now, for which car seats to buy, I suggest going right for the boosters at this point. My neice has a GRACO booster that seems pretty sturdy. HTH!