Gaza has long been subjected to food insecurity; however, little was known about the influence of food insecurity on the nutritional wellbeing of schoolchildren. To fill this gap, the UN Relief and Works Agency for Palestine Refugees in the Near East (UNRWA), which provides humanitarian relief to Palestine refugees, assessed the nutritional status, diet, and food security of refugee children about to enter first grade (aged 4-10 years, mean age 72·1 months) in mid-2023 during a required health examination. As part of an annual School Entrance Health Examinations that began in May, a cross-sectional food security and nutritional assessment was added from July 8, to Sept 7, 2023, during which children being examined at six study-designated UNRWA clinics across Gaza were systematically sampled (in a 1:4 ratio) and parental or guardian consent sought for their participation. Household food security was assessed by a seven-point Arab Family food Security Scale score, and respondents were asked about family receipt of food assistance. The 1-week meal patterns of the children were probed, and intake frequencies of 49 foods in the past month categorised into ten nutritious food groups to assess diet diversity. The weight, height, and haemoglobin concentrations (assessed with a photometric analyser) of the children were measured. The UNRWA Research Review Board approved all study procedures. Approximately 34 000 children underwent the annual School Entrance Health Examination in Gaza in May, 2023 and approximately 16 000 children were estimated to have completed the additional food security and nutritional assessments from July 8, to early Sept 7, 2023, of whom 3814 were systematically sampled at six UNRWA clinics across Gaza, with 3229 (84·7%) parents or guardians consenting for their children to participate. 3155 were interviewed about household food security with a seven-point Arab Family Food Security Score, and 3212 were asked about food assistance receipt. 2694 (83·9%) of 3212 households were on food assistance, 787 (24·9%) of 3155 were classified as food secure (0-2 points), 1025 (32·5%) were classified as moderately (3-5 points) food insecure, and 1343 (42·6%) as severely food insecure (6-7 points). 219 (28·5%) of 768 children reported missing breakfast and 213 (28·4%) of 750 reported missing dinner in the food-secure group, 438 (47·2%) of 928 reported missing breakfast and 426 (45·6%) of 934 reported missing dinner in the moderately food-insecure group, and 956 (75·5%) of 1267 reported missing breakfast and 951 (74·8%) of 1272 reported missing dinner in the severely food-insecure group. Lunch was missed daily by 30 (3·8%) of 786 children in the food-secure group, 54 (5·3%) of 1023 in the moderately food-insecure group, and 193 (14·5%) of 1334 in the severely food-insecure group. Diets were poor in dairy items, meat, poultry, fish, pulses, eggs, and vitamin A-rich vegetables and fruit, and 2225 (68·9%) of 3229 children did not consume a minimally diverse diet every day (≥5 nutritious food groups). 72 (2·5%) of 2913 children had stunting and 129 (4·4%) of 2913 had wasting (less than -2 Z scores), and 963 (29·8%) of 3229 had anaemia (haemoglobin <11·5 g/dL). Boys and girls were similar in their diets, anthropometric Z scores, and prevalence of anaemia. Gazan families with children about to enter first grade were food insecure and reliant on food assistance, possibly protecting the anthropometric status of the children, whose diets however lacked diversity. Japan Ministry of Foreign Affairs and the Vitamin Angels Alliance, USA. For the Arabic translation of the abstract see Supplementary Materials section.