The Charlotte, N.C., company is recalling the Coccoro, Zeus Turn and Zeus 360.
The National Highway Traffic Safety Administration says the seat straps don't meet minimum strength requirements. If there's a crash, children may not be properly secured.
A company spokeswoman says the seats are still safe to use because the harness as a whole meets safety standards. She says one part of the harness that includes a plastic button failed strength tests. Seats made after January 2013 don't have the same problem.
Combi will notify registered owners and send out free harness replacement kits starting in February. Owners can contact Combi at (800) 543-7734.