THE NSW opposition says parents should lock up their children when amateur gunmen start shooting in the state's national parks.

The shooters will start from the April school holidays.

The government will allow licensed shooters to shoot feral animals in national parks from April, instead of March, while it continues consultations over the implementation of the controversial move.

The move has raised concerns that visitors to parks risk being accidentally shot by hunters.

Opposition environment spokesman Luke Foley said April was not the time to introduce "amateur gunmen" to parks.

"There's no safe time to bring amateur hunters to our state's national parks that receive 35 million visitations a year," Mr Foley told reporters today.

"But the very, very worse time is the school holiday period.

"It stands to reason that any new program ... is going to have flaws and problems in its early days.

"My message to parents (is) lock up your children if Mr O'Farrell is going to start introducing amateur gunmen to national parks this April school holidays."

Environment Minister Robyn Parker is expected to announce on Wednesday that the program's funding over five years will cost taxpayers at least an extra $19 million.

The money will go towards 14 additional National Parks and Wildlife Service coordinators, new signs, staff training and education programs for shooters.

Mr Foley said $19 million would have gone a long way to professionals getting rid of feral animals in national parks.

NSW Greens environment spokeswoman Cate Faehrmann said no amount of money would make amateur shooting in parks safe.