There’s normally an open house at the kids’ club early on the first day; parents can an have a look too. On a past cruise my then-15 yr old went right up to the Vibe. He was the 3rd person there and quickly made acquaintance with several other kids. He said that by being one of the first there, it made it less awkward joining in later since he already recognized a few other kids. Five years later he still chats with a couple of them....small world these days! Maybe this strategy would work for your son & daughter.