If a child doesn't yet have permanant teeth, is it nessecarry to get a root canal performed?

No: I am not a fan of root canals so my answer would be no. However a dentist may be able to provide a more complete answer.

Sometimes: Your child's permanent teeth are all present under the gums. Infected baby teeth can infect and harm the underlying permanent teeth. Early loss of baby tooth can cause other teeth to shift and create malocclusion. Root canal treatment (pulpotomy) is often better treatment option than extraction and space maintainer.