Introduction This study aims to identify the prevalence and pattern of bruises in preschool children over time, and explore influential variables

Methods Prospective longitudinal study of children (<6 years) where bruises were recorded on a body chart, weekly for up to 12 weeks. The number and location of bruises were analysed according to development. Longitudinal analysis was performed using multilevel modelling.

Results 3523 bruises recorded from 2570 data collections from 328 children (mean age 19 months); 6.7% of 1010 collections from premobile children had at least one bruise (2.2% of babies who could not roll over and 9.8% in those who could), compared with 45.6% of 478 early mobile and 78.8% of 1082 walking child collections. The most common site affected in all groups was below the knees, followed by ‘facial T’ and head in premobile and early mobile. The ears, neck, buttocks, genitalia and hands were rarely bruised (<1% of all collections). None of gender, season or the level of social deprivation significantly influenced bruising patterns, although having a sibling increased the mean number of bruises. There was considerable variation in the number of bruises recorded between different children which increased with developmental stage and was greater than the variation between numbers of bruises in collections from the same child over time.

Conclusions These data should help clinicians understand the patterns of ‘everyday bruising’ and recognise children who have an unusual numbers or distribution of bruises who may need assessment for physical abuse or bleeding disorders.