Some children shouldn't be placed for adoption according to Dr. Mike Davies, an independent consultant psychotherapist.
The comment was made during the Children and Young People Committee's inquiry into adoption, on 23 May 2012.
Whilst giving evidence to the inquiry, Dr Davies said that a "very small proportion" of children have experienced such difficulties that they shouldn't be put into the adoption system.
Dr Davies explained in a publication handed to the committee, that "there seems to be an assumption in social work agencies that younger children who have suffered considerable adversity, can by virtue of the fact that they are still very young, have their needs best met in an adoptive family."
He challenged this view and expressed his concern with the lack of screening of the child's potential attachment problems prior to deciding his or her future placement.
Attachment problems range from mild anxiety and separation problems to severe challenging behaviours, as well as an absence of empathy and severe temper outbursts.
Barnardo's Cymru and St David's Children Society also gave evidence during the inquiry.
The Welsh government is considering the advantages of creating a national adoption agency that would take over the work that is currently done by local authorities, a move supported by both charities.
The committee also heard evidence from the Welsh NHS confederation.