This arrangement is hard to get information on and seems to vary from county to county. The main benefit is parents can get nappies for free if they have a child with special needs.
You can only access the scheme when your child reaches the age of 3 or over because up to this all children need nappies. The supply is restricted to 62 nappies per month & is administrated by your local Health Nurse.
You should contact your local Health Centre and be persistent as the scheme does exist but few know about it.