A fantastic exhibition project (in situ in Budapest, but accessible online in an older version in Hungarian, English and Dutch) tells the story of the 1920s campaign to host Hungarian children to the Netherlands, Switzerland, Sweden, the UK, Belgium, and elsewhere, to help them escaping from the post-war economic and social crisis in Hungary.
Thanks to the campaign, more than 60,000 children returned home well-nourished after a few months (sometimes even years) abroad; however, some of the children stayed in the host country for the rest of their lives, strengthening the relationships between Romania and the host countries.
You can find the exhibition here: https://www.varmuzeum.hu/childrenstrains.html
Needless to say given the international outlook of the story, Archives Portal Europe hosts many collections around Europe dedicated to the Hungarian children refugees, and other stories (Russian and Spanish Refugees)
HUNGARIAN REFUGEES
DUTCH ACTION CHILDREN'S HOMES HUNGARY (Nationaal Archief, 1922-37): http://www.archivesportaleurope.net/ead-display/-/ead/pl/aicode/NL-HaNA/type/fa/id/2.19.013/search/0/hongarije+kinderen
Hungarian children before their departure to Hungary at the Staatsspoor station in The Hague (Internationaal Instituut voor Sociale Geschiedenis, 1927): http://www.archivesportaleurope.net/ead-display/-/ead/pl/aicode/NL-AmISG/type/fa/id/https_COLON__SLASH__SLASH_hdl.handle.net_SLASH_10622_SLASH_COLL00476/unitid/https_COLON__SLASH__SLASH_hdl.handle.net_SLASH_10622_SLASH_COLL00476+-+16/search/0/hongarije+kinderen
National Child Protection League and Children's Sanatorium Association (Magyar Nemzeti Levéltár Országos Levéltára, 1918-50): http://www.archivesportaleurope.net/ead-display/-/ead/pl/aicode/HU-28947/type/hg/id/K/unitid/K_319/search/0/Gyermekv%C3%A9delmi+Liga
Children from Hungary, Austria, and Germany sheltering in Belgium (National Belgian Archives, 1920-62): http://www.archivesportaleurope.net/ead-display/-/ead/pl/aicode/BE-A0510/type/fa/id/BE-A0510_004812_004133_FRE/unitid/BE-A0510.1645+-+244+-+249/search/0/enfants+autrichiens
HELP FOR RUSSIAN CHILDREN REFUGEES IN THE POST-WAR:
Help for Hungry Russian Children (La Contemporaine, France, 1919-39): http://www.archivesportaleurope.net/ead-display/-/ead/pl/aicode/FR-00000028858/type/fa/id/FR_920509801_LC_Musee_9_1_Maitre_Coll_Musee_Aff+18_39_L3_1.xml/dbid/C639948487/search/0/enfants+russes
Collections from the Belgian State Archives:
HELP FOR SPANISH REFUGEES:
Spanish exile in Belgium, France, and the UK (Centro Documental de la Memoria Histórica): http://www.archivesportaleurope.net/ead-display/-/ead/pl/aicode/ES-37274-CDMH1/type/hg/id/ES-37274-CDMH/unitid/ES-37274-CDMH-UD-12734444/search/0/ni%C3%B1os+B%C3%A9lgica