Exposure to air pollution (AP), particularly fine particulate matter of ≤ 2.5 µm (PM2.5), is an increasing public health concern, especially for the lung health of children. Our study aimed to evaluate fractional exhaled nitric oxide (FeNO) levels, spirometry abnormalities, and the burden of respiratory symptoms in children sensitive to AP. A cross-sectional study was conducted from December 2022 to January 2023 with stratified random sampling performed on 170 grade 6 and 7 students at two schools, one each in Binh Tan and Binh Chanh district, randomly selected from low and high air quality index areas in Ho Chi Minh City. FeNO levels and spirometry readings were obtained, and the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire was used. PM2.5 concentration in schools were measured hourly outdoors and indoors. The results revealed that PM2.5 concentrations outside and inside schools in Binh Chanh district were higher than in Binh Tan district, at 62.2 µg/m3 compared to 30.5 µg/m3 (p < 0.001) and 47 µg/m3 compared to 29.1 µg/m3 (p < 0.001), respectively. Over 50.0% of the population exhibited nasal symptoms, and 13.5% complained of wheezing in the previous three months. The average FeNO level was 7.9 ± 8.7 ppb, with 5.3% of children having FeNO levels above 25 ppb. Using Z-score, spirometry abnormalities were shown to include PRISm at 2.3%, dysanapis at 1.8%, and obstruction at 0.6%. Linear regression analysis revealed a weak negative correlation between %VCmax PRE (r = −0.202, p = 0.008) and %FVC PRE (r = −0.155, p = 0.043) with PM2.5. No correlation was found between FeNO and PM2.5 concentration. Children were exposed to PM2.5 both indoors and outdoors. For symptomatic and lung dysfunctional individuals, long-term follow-up is necessary to implement appropriate interventions.