bringing an old topic topic to life.... 2 (very long) subjects:
1) Griffith took over Guts' and Caska's baby. Theres no doubt about it. He refers specfically to his body when he and Zodd meets Guts at hill of swords, and Guts seems to have an affect on his kid's body even though Griffith, who is in control of the body, had rid himself of any hindering feelings towards Guts.
Remember, Caska gave birth to some kind of (evil) spirit - a sort of ghost - that can be categorized with the badies that haunts Guts and them every night. This spirit (I'll call it "Gutska" for now ~_~) followed and haunted Guts during the 2 years after the eclipse. He warned Guts about Caska's escape and even protected Caska in the tower. So regardless of how Guts feels about Gutska... the kid doesn't want to hurt his parents. I think this will affect the fight between Guts and Griffiths.
2) The kid on the beach is a huge mystery, and his likeness to Caska (and arguably Guts) is a big question mark, and this is all done on purpose to create more interest and argument.
One thing you guys didn't mention is that after Guts fought the crocodiles and the elepant sea monster for the first time, his Berserk-self was about to attack the group until a light spirit thingy stopped him, saying "not an enemy" (Vol 28 chap242-243). People generally think that's Schierk's work, but I'm SURE that the spirit figure was the kid and Schierk was only able to reach Guts after the kid broke a hole thru the darkness created by the Berserker armour.
Evidence that the kid on the beach is the spirit that stopped Guts:
->You'll notice that whenever Schierk does her "work" in the spiritual realm, she retains her physical form for the most part (hat, face, mantle, arms-> all intact). In fact, when her master, forgot her name, protected the group from Gurunberd, SHE also retains her humanly feature, whereas this light spirit thingy looked more like an elemental. Its form can be compared to the spirits in Serpico's sword or even the 'Angels' that Schierk calls upon for help, which leads me to believe that it is NOT Schierk but something completely different - a non human spirit that is GOOD.
-> Guts suspected the same thing (Vol 28 chap243 page156). Gut's was wondering what the hell that spirit was too, and he didn't automatically assume it was Schierk; his first thought was the kid.
The problem for everyone is that he resembles a manifestation of Caska's utmost desire - her baby, and fittingly so too, because she gave birth to Gutska 2-3 years ago and BAM a 2-3 year old kid that looks just like her pops out of the ocean. Coincidence? I'd also point out that Miura reveals him RIGHT as the skull knight was talking about what Caska's desires are.
The things that I would semi-confidently say about the kid on the beach is that A) he has special powers, explaining the strange OD that Schierk senses on him B) he saved Guts after the fight on the beach, and C) he's some kind of spirit that is probably good. Could he be related to the Elf king? Maybe he's a spirit of the sea?