Careful with kids! You'll screw it all up if you try to buy a 4 year old their own ticket alone.
Honestly, I do not think the headache is worth 5%

Multiple tickets, multiple legs of the journey, on multiple people, and still paying with the CC. In fact, it's less than 5% if your ticket costs more than $150.
Is saving $7.50 per ticket really worth it?
I'd find the savings elsewhere...