Disabled Child Elements and gaps in DLA

I have several people I am working with who should have been been getting the disabled child elements in their UC for many years.
I am aware the legislation supports backdating to the award of the qualifying benefits. Can this also happen if there have been gaps in the DLA awards due to needing to reapply etc. Can they get backdated amounts of the DCE for any time that the qualfying benefit was in payment.
If so, practically how would you ask for this - would you do a change of circ’s with the first date DLA was awarded then add a message in the Journal asking a DM to backdate to then and then provide the subsequent dates the DLA stopped and then started again so the DCE can be applied to those periods too
Many thanks