It is virtually impossible for parents to treat all of their kids exactly the same. There will always be lessons learned with the older children that will influence how they treat the younger ones. Parents might learn that they’re being too lenient with their older kids and start implementing a more disciplined parenting style for their younger ones. The opposite is more likely to happen, with parents having incredibly stringent rules for their older child and being more chill with the boundaries for the younger child. 

Just because you can’t technically treat every child the same doesn’t mean you shouldn’t make an effort to be fair and equitable. There’s no reason a 13-year-old should get significantly more Christmas presents than their 15-year-old sibling. You shouldn’t give privileges to a 5-year-old that you would not allow your 8-year-old to have. Children are always paying attention, and they will internalize unfair treatment.