I was wondering is it necessary for a child to have a spacer put in after a tooth extraction?

Sometimes....: Every situation is different, so it is best if you discuss your child's specific situation with the dentist. The need for a spacer depends on age of child, which tooth(teeth) are involved, why the original tooth was lost, and other factors. All of these have to be weighed to decide if a spacer is needed.

That depends: That depends on which tooth was extracted and how old the child is. If it is one of the front 4 teeth then space maintainer is not usually needed. If it is a back tooth it will depend on how soon the permanent tooth is due to erupt. Your child's pediatric dentist can help guild you in making the correct decision for your child.

Maybe: Much of this answer depends upon where the tooth that was extracted is and the age of the child. Consult your dentist to get a true answer for your specific child.