If you have bought a mac for yourself, not buying one for your kid just seems wrong. In my opinion a parent shouldn't spend more money on himself than the rest of the family. Each family member does his own part of chores, whether it's a job, housekeeping or studying. Rewards should be given out fairly. Otherwise don't be surprised when your kids don't support you in your old age.
Children need to learn the value of things and the hard work it takes to get those nice things. I'm not saying you buy your child a broke down laptop, but you don't buy them a maxed out Macbook either.
And a lot times people buy MacBook pros because they need something reliable for work. Using your logic, parents shouldn't buy a BMW unless they buy their child one as well.