My vampire sim delivered twins and I did a "dry run" to see how vampirism works with children. It seems that children age normally (3 days infant, 7 days child, 14 days teen on normal life span), have normal hunger needs and do not display any vampire traits (running fast, fast learning, burning in the sun) until aging up to young adult. However, they do show up in the relationship bar with the red line around their picture like normal vampires.
Off to play again, this time letting the children age up normally. I'll post some pics later.