You just need to ask them to check for the DR haplotype. HLA testing is more expensive when you check more haplotypes - there any many to check. Its a poor analogy, but when looking at a car engine, you can just check the oil, or you can also check the radiator, spark plugs and carburetor.
If the result is DR5 on one side and DR7 on the other, then the child has the same risk as if they simple had one DR3. Its complicated why thats true, you can read it in the above file.
If the child has NEITHER of the above scenarios, it is very very, very unlikely they will ever get celiac disease.
Most good commercial labs can run HLA, its much more common of a test than regular celiac testing (endomysial test).