shtarky, as a parent you have to realize that NOT each child is treated equally. Different children have different needs. Just like you wouldn’t put one child in therapy bec another child is getting it, similarly, some children need more leniency while others need a firmer hand etc. Parents need loads of Siyata Dishmaya to determain exactly what each child needs while at the same time avoiding jealousy.
This of course is the same advice we get from a famous Chazal, learned from Yaakov Avinu…80