Air pollution has been recognised as the single biggest environmental threat to human health within the European Union (EU). Indoor air pollution has received less attention than outdoor air pollution, even though we spend most of our time indoors. It is associated with a variety of short- and long-term health effects. These include allergies and asthma with a key role for the exposure to bioaerosols and synergistic interactions between chemical and biological pollutants. Given the dramatic rise of allergic diseases, the prevention of symptom exacerbations and the new onset of disease are of great importance, particularly for vulnerable populations such as children. The lack of a unified EU-wide approach involving all stakeholders represents a major unmet need. The EU-funded IDEAL Cluster comprises seven research projects to advance knowledge on indoor air quality (IAQ) and its impact on health, inform policies and thus promote healthier indoor environments. The ‘SynAir-G’ project forms part of this cluster and was launched in 2022 with the participation of 18 partners from 11 countries. It focuses on schools to explore synergistic interactions between chemical and biological pollutants based on the hypothesis that these modulate major health effects. SynAir-G includes the development of low-cost sensors, collection of health outcomes, modelling of pollution dynamics and the development of mitigation solutions. The knowledge will be circulated to all stakeholders and the public aiming to establish standards and health-based guidelines. The scope of this position statement is (1) to review the current evidence on indoor air pollution, its impact on health and particularly on children with allergies and asthma; (2) to give an overview of the European regulatory framework; (3) to describe knowledge gaps, challenges and unmet needs; and (4) to present SynAir-G′s project goals and propose a roadmap to improve IAQ for children with asthma and allergies.