Rarely will a helicopter ride service offer child prices or reductions for small children. The prices you see are prices per seat - not prices per adult or child.
So you will have to pay full price for a child as they would need to sit in there own seat.
If you're bringing along a toddler under 2 years; then there's no price associated with those 24 months and under, so they fly free.
However, toddlers will need to be fastened onto your lap in order to qualify as a free flight.