One GFCI outlet to protect them all
If you can locate the outlet at the head of the chain, then you only need to replace that outlet. Just make sure the the incoming power is connected the the LINE terminals and the downstream outlets are connected to the LOAD terminals. The instructions included with the outlet should explain this.

Alternatively, if the only thing on that circuit are your kitchen outlets, you could replace the breaker with a GFCI breaker.