I reckon that taking painkillers is a habit best avoided, especially for children. - Don't you agree? - And so I'd suggest not getting into the habit of giving babies and toddlers liquid paracetamol or similar after they have had an injection or taken a tumble. When I was a little girl it was unheard-of for children to be given pharmaceutical drugs to stop their tears. Instead their mothers would give them a kiss and a cuddle, and a special kiss on the poorly place to 'kiss it better'. Happily,unlike drugs, a kiss and a cuddle have no adverse side-effects. I offer this little couplet:
Give a kiss and a hug,
Not a painkiller drug.
Older children can be encouraged to be a 'big boy' or a 'big girl' when they experience pain and to be rewarded with approval for their stoicism. This could serve them well in later years. Our society is too dependent on pharmaceutical drugs, which, on the whole, do far, far more harm than good.