You are gonna hear a lot about how safe and wodnerful Britax is, but really, most car seats are very safe..IF THEY ARE INSTALLED PROPERLY!! So, if you are concerned, go check that to get some peace of mind. Lots of fire stations and even children's hospitals have car seat inspectors that would be willing to help you out! And, I would put the 4 year old back in a harness for sure! That is the thing I think is the most unsafe:) They are just not mature enough to sit properly all the time, and really, if something happens and the seat belt comes apart in crash, then your 4 year old goes flying. If she is in a car seat, at least she stays buckled to the seat. Better yet, install it with the latch system!! I am considering buying the new Graco (I think it is a Nautilus) and using that one for my 2 year old. Good luck..you are not a bad mom...money does not buy parenthood! For me it is a lot like knowing that a Honda mini van may have better crash ratings than my Ford Freestar, but I cant afford the Honda, so I do the best I can with what I have. My kids are as safe as I can make them!! ~A.~