"It's bad form," Child Matters chief executive Anthea Simcock said.
"He's certainly not an appropriate person to be heading up any show for children anymore, given what we now know about him."
It was "unfortunate" Harris was narrating the show, and parents would have no trouble recognising him, she said. "It is a distinctive voice."
Ms Simcock said it was odd the show made it to air, considering Sayle's high-profile replacement of Harris nearly 18 months ago.
Sky said it was investigating how narration featuring the child molester could make it to air.
"At this point in time it looks like there may have been a Rolf Harris episode go to air in error," Sky spokeswoman Kirsty Way said.
This was despite Sky saying it implemented a policy months ago to remove the disgraced entertainer's episodes from its schedule.
"The policy was to pull them all and only play the episodes that were voiced by [other narrators]," Ms Way said.
Harris' victims allegedly included several New Zealanders, some of whom spoke to police running the Operation Yewtree investigation into sexual abuse.
Cabinet minister and former broadcaster Maggie Barry spoke out about Harris, saying he groped her when in New Zealand recording an interview for a radio show.
Even before Harris' conviction for sex offences, Britain's Channel 5 pulled all programmes he featured in from its schedules. And this month, the Governor-General of Australia stripped Harris of his honours.
Harris was jailed for five years and nine months for a dozen indecent assaults on four victims between 1969 and 1986.
