How much do the tickets cost children of the ages of 17,16,15 and one adult?

You will have to pay full unfortunately

Kids are 9 and under so you will be paying full price for all of your tickets. Multi-day passes will reduce your daily ticket rate. One thing to note: if you want to take the Hogwarts Express you will have to purchase the park hopper tickets.

for single park one day passes it's $115 per adult, $110 for a child. Hard to tell what's a "child". first tickets page says 0-9, next page says up to 17. either way only $5 cheaper for kids. Park to park passes are more expensive, means you can hop between the multiple parks in one. Buying tickets for multiple days makes a per day rate cheaper.