Research has shown that online security warnings are frequently ignored or misinterpreted by even experienced adult users. Children may be particularly vulnerable because they are not always aware of the risks associated with online threats. Existing work relating to cybersecurity warnings has been done with adults and there are few recommendations for children. We explore this research gap through two user studies with 22 children aged 10-12 years old and with 22 adults. We compare children and adults' perception of warning design parameters (signal colours, symbols, and words) in the context of cybersecurity warnings. Our findings suggest that while there are many similarities in how both groups interpret the signal items, differences exist which should be taken into consideration when designing for children. We adapt existing warning design guidelines by Bauer et al. to provide recommendations for warnings that effectively communicate risk to children.