Thanks for your query.
You are right about the fact that both girls have influenza
like illness .
It seems they have developed myositis
( inflammation of leg muscles) which is a known association of influenza & similar viruses.
There is no need to panic & continue giving brufen
syrup in appropriate doses along with plenty of oral liquids & bed rest
Both will improve in 3-4 days.
Wishing them speedy recovery.