If there was no German child support order made, and more important, none requested by either party, then the jurisdiction in which the obligor/paying parent resides when the first child support order is made would control the duration of child support -- unless the paying parent submits to the jurisdiction where the other parent and child reside.
If your husband is sued for child support in Mississippi, he must be VERY careful to not inadvertantly submit to Mississippi jurisdiction, or he can be held to a child support obligation until the child is 21 years of age, under MIssissippi law.
Avoiding personal jurisdiction is tricky, so if he's sued, he needs to hire a Mississippi lawyer to "challenge personal jurisdiction." For a family law attorney referral, see: http://www.abanet.org/legalservices/lris/directory/main.cfm?id=MS and www.martindale.com.
Hope this helps.
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