Background The COVID-19 pandemic has had wide effects on child health globally. Increased prevalence of childhood obesity has been observed by a number of countries during the pandemic. The absence of a formal societal lockdown during the pandemic, made Sweden stand out compared to other countries. This study aims to examine changes in BMI among preschool children in Sweden before and during COVID-19 pandemic. Methods Retrospective population-based cross-sectional study, with longitudinal follow-up for a portion of the children. The study included 25 049 children from three Swedish regions, with growth measures at 3- (n = 16 237), 4- (n = 14 437) and 5-years of age (n = 11 711). Care Need Index was used as a socioeconomic parameter at health centre level. Results There was an increase in BMI in children aged three (P = 0.028) and four (P<0.001) during the COVID-19 pandemic. Obesity in 3-year-old girls increased from 2.8% to 3.9%. Four-year-olds increased in obesity, and overweight (girls) and the prevalence of underweight decreased in boys. No change in BMI was observed in 5-year-olds. Children in areas of low socioeconomic status had higher risk of obesity. Conclusions Overweight and obesity increased among 3- and 4-year-old children in Sweden, findings that were accentuated in children attending child health centres in areas with lower socioeconomic status. The COVID-19 pandemic is likely to have affected health behaviours negatively in Swedish preschool children. Our results expose the need for extended efforts directed to prevent childhood obesity, especially targeting lower socioeconomic areas.

Aim To explore the relations between asthma, allergies and mental health problems in preschool children, aged 3‐5 years. Methods In this cross‐sectional Swedish study, we used data on 4649 children in Uppsala municipality whose parents and preschool teachers had responded to questions measuring asthma and allergies, and the Strengths and Difficulties Questionnaire (SDQ) for assessment of mental health problems. Logistic regression models were used to explore the relations between asthma and allergies and mental health problems. Results Children with asthma (8.5%) had elevated odds of having emotional symptoms as rated by parents (OR: 1.34; 1.02‐1.76) and teachers (OR: 1.44; 1.09‐1.91). According to parents’ ratings, these children also had elevated odds of showing mental health problems in general according to the SDQ total score (OR: 1.42; 1.05‐1.94). Children with food allergies or intolerance (4.4%) only had elevated odds of having emotional symptoms (OR: 1.64; 1.16‐2.33), as reported by parents. These results remained significant after adjustment for parental background factors. Conclusion Preschool children with asthma and food allergies or intolerance are at risk of having concurrent mental health problems. Mental health problems should be assessed in children with these disorders. Adequate support and/or referral to specialised services should be offered when needed.