i believe most dogs don't understand the concept of "kissing" and most shepherds (not all, but most), tolerate it but truthfully don't really like it. i think you dog is demonstrating remarkable restraint, but she is telling your son (and you), in no uncertain terms that she feels her space is being invaded. i would immediately stop the kissing behavior on your son's part, and all body contact between them, maybe i'd even tell him to (for a while) let her approach him when she wants his attention. then i'd be very vigilant and watch for ANY other signs of this behavior on her part. and don't blame her if she's not fond of the kissy/huggy attention, she's a shepherd. if she's aggressive to him under any other circumstances, that's a different story. but i do think she's demonstrating remarkable restraint and is giving out a definite message in the only polite way she knows.
mom to seraphina blue & the cashman
miss jeni-take-a-ride, rescued 7/07
shangri la's great white caesar, rescued 4/09
hearthside's cinderfella (RIP 4/20/09)
shep von bellefontaine (RIP 6/9/10)
voodoo lily (dsh) & cricket (african grey)