Its a clear fishy trap and its the way how they are trying to plant malware. UNICEF is a non profit organization and they haven't launched any app like his. They have got only social media accounts and real website where they post all heir activity reports.
UNICEF website:
https://www.unicef.orgI will suggest OP to submit report allegations of fraud, abuse, waste and mismanagement by sending email here;
integrity1@unicef.org