Can we reuse team photos for something new, like a sponsor's advert or a fundraising flyer?

Only if the new use is compatible with the purpose the photos were collected for, or another exception applies.

• Photos must be collected for a specific, explicitly defined and lawful purpose related to the club's activities (s13(1)).
• Further processing must be in accordance or compatible with that purpose (s15(1)). To judge this, the club must consider the link between the old and new purposes, the nature of the information, the consequences for the child, how the photos were collected, and any contractual rights (s15(2)).
• The new use is not incompatible if a competent person (parent or guardian) consents to it (s15(3)(a)).

Because the photos are of children, the new use also needs its own section 35(1) ground, normally the prior consent of a competent person (s34-35). If the original consent covered only club match reports, ask parents again before using the photos in a sponsor's advert or on fundraising material.

Source: POPIA (Act 4 of 2013) ss 13, 15, 34-35.