My feeling* is two meter wide lanes is sufficient unless you plan to host major national or international competition. Considering the second pool is more or less a "kiddie" pool I'm assuming this is not the case. One advantage of the 2.5 meter lanes would be that you might be able to configure the pool as ten lanes for training purposes. The bottom and end markings would be useless with the ten lane setup, of course.
* with the caveat that I'm on no way an expert on pool design!