Accompanying an Additional Child on the Bus

When I travel on public transportation with two children under the age of 5, is it permissible to ask someone on the bus to be considered the accompanying adult for one of the children, in order to save the cost of the fare? Must I ask him explicitly, or is it enough that there is a person on the bus without children, whom it is reasonable to assume would agree to be considered an accompanying adult?
(At the time I travel with the two children, the bus is full of women and girls from our community who would undoubtedly agree to serve as an accompanying adult.)

Hello and blessings 

One may ask one of the passengers to be the accompanying adult for the second child. 

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