Holly Wells and Jessica Chapman were killed by a school caretaker in 2002
The man whose inquiry into the Soham murders led to new child protection procedures is calling for a re-think on a proposed vetting scheme in schools.
Sir Michael Bichard fears people who occasionally visit schools, such as authors, actors and entertainers, may have to join the database.
He warned: "We must have proportionate arrangements" and "mustn't over-react".
The Home Office said anyone with "regular" or "intense" contact with children will have to register.
"Regular" is defined as more than once a month and "intense" as three times a month or more.
But Sir Michael told the Independent newspaper: "What I didn't want was a disproportionate response. I made it very clear that I didn't want parents to have to check relatives before they could put their children in their care for baby-sitting and things like that."
The Vetting and Barring Scheme (VBS) will apply in England, Wales and Northern Ireland and registration will become compulsory from November 2010.
A separate but aligned scheme is being set up in Scotland.
The government estimates up to 11.3m people in the education, care and health industries will eventually be on the database.
The scheme does not replace checks by the Criminal Records Bureau (CRB). The register will involve a CRB check but not every conviction will led to a person being barred.
The Bichard Inquiry looked into child protection after the murders of Holly Wells and Jessica Chapman in 2002.
They were killed by school caretaker Ian Huntley in Soham, Cambridgeshire.
One of Sir Michael's key recommendations was a registration scheme for those wishing to work with children or vulnerable adults.
Sir Michael said the proposed register contained a number of issues which "needed to be looked at again".
"If you visit one school in January, and then don't visit that school again, but visit another school in February and another in March, is that frequent or intensive?
"I think that's something which might merit reconsideration," he said.
He told the newspaper he had taken his concerns to Sir Roger Singleton, the chairman of the Independent Safeguarding Authority, which is responsible for assessing who should be included on the database.
In October, the scheme to vet everyone who wants to work or volunteer with children or vulnerable people will begin - becoming compulsory in November 2010.
There will be a one-off registration fee of £64 for those seeking employment but it will be waived for volunteers.
Philip Pullman said he had been going into schools for years
Several high-profile authors, including Philip Pullman and Michael Morpurgo, have threatened to stop visiting schools in protest at having to register with the scheme.
Pullman, author of fantasy trilogy His Dark Materials, said: "Why should I pay £64 to a government agency to give me a little certificate to say I'm not a paedophile?"
But Sir Michael said the authors' response had been "disproportionate".
"I don't have a lot of sympathy for people who say that just because they have to go through a checking process, somehow it's being implied that they are a child molester," he said.
A Home Office spokesperson said regulations had to be "rigorous" and added:
"From 2010 anyone who works or volunteers regularly in a school will need to be checked and registered with the scheme.
"The rules do not discriminate on the grounds of an individual's job.
"People making visits to schools or undertaking occasional work will be exempt from these rules, but those who have frequent access to children will have to be checked.
"We believe this is a common sense approach, and what parents would expect."