Regulating those in care roles in the residential children's sector was a recommendation from the Independent Inquiry into Child Sexual Abuse (IICSA) in April 2018.
This inquiry was concerned by the lack of professional registration in the sector and said that a register should be phased in over time, with priority given to children's home managers.
But in its response to a Department for Education (DfE) consultation on the plans, the ADCS raises fears that the move could impact on homes' costs as well as their recruitment and retention of staff.
The ADCS's response "urges the government to consider the recommendation's impact on the recruitment and retention of care staff if professional registration were introduced".
It adds: "It is important that children's homes have a rich diversity of care staff and there is a risk that this proposal may have an adverse impact on recruitment if not carefully considered."
Increased costs incurred by homes through registration is raised as a particular concern by the ADCS.
It says that any registration must not duplicate existing assessments of staff and warns that the move could disrupt the running of homes while time is taken to ensure staff adhere to the register.
"Registration of managers and care staff, if underpinned with a code of practice and professional standards, would enable greater consistency across the workforce, however, this would need to be implemented in a way that does not duplicate the assessment of fitness to practice in order to limit potential costs," states the ADCS response.
"Further, if professional registration is introduced, this may require re-registration of staff on a periodic basis and could be resource intensive and have financial implications. The costs associated with a requirement for children's homes staff to be registered will likely be passed onto the local authority.
"At a time when the cost of placing a child or young person in an independent children's home is very high, ADCS is concerned that additional costs incurred by local authorities will place extra pressure on already heavily reduced budgets."
The ADCS also calls into question existing training and qualifications, of Level 3 for care staff and Level 5 for managers.
The ADCS says this is not always achieved by staff. In addition, homes are providing alternative training, that many find "equally valuable and also suited to their needs", adds the response.
The DfE is being urged to consider a system where equivalent qualifications can be transferred by staff between different children's workforce roles.