Service may be made on a person who resides with the party named, provided that the person served is of suitable age and discretion. There is no bright line rule as to what age constitutes this, instead the court will look to see if the circumstances are sufficient to assure that your child would have been competent enough to give you the papers. There is no legal obligation on the process restricting this behavior, although not professionally courteous, it is legal.
I agree with Mr. Russ and the process servers have a tough job, but putting this in an envelope wouldn't be too much to ask. The age rule is fuzzy and we always follwed the rule if they are home alone that is old enough. Now I always start with the sheriff's civil department and don't use private servers unless there is a problem the sheriff can't handle.
In order for service to be proper, it has to be on someone that is 18 or older and residing with you. This will not be proper service but in my opnion also very careless of the process server. You would have to find out what company they are from and contact them to lodge a complaint.