Apples are thought to be the plant most capable of variation from seed in all the plant kingdom. So what you will get from your pips could be almost anything, but almost certainly not a Pink Lady. It could be a new variety of worthwhile apple or more likely a 'spitter'. (Take a bite and spit it out!).
Next point is that it takes about 5 years for a tree to produce fruit, so you have a longish wait.
Finally apple trees on their own roots can grow anywhere up to 60 feet tall! (In time).
It is still worth trying though, if only to keep your son's interest in the process.