The Association of Play Industries (API) spoke out after reports that Wandsworth council was in talks with private firms to take over the running of two of its three adventure playgrounds.
The Conservative London borough needs to save £30m.
API public development officer Alan Steiner said:
"Privatising may bring in investment but I can't see how Wandsworth can do it without charging.
"Some ares of the borough are quite deprived. Having to pay £3.50 or £5 to get into these playgrounds could exclude some children."
API chairman John Croasdale said:
"We recognise some staffed play areas may need to charge for children to play, but families look to their local authority and their Government for free and accessible play spaces."
Wandsworth did not comment on York Gardens and Kimber Road Gardens playgrounds other than to say:
"There are no firm proposals at the moment."
Earlier this year Wandsworth announced plans to charge £2.50 for children to use Battersea Park adventure playground. It later backed down after parents threatened legal action.