Lots of firsts this week: jolly jumping (well, mostly swivelling on tiptoe so far), standing supported (looks delighted every time), sitting up (with help), rolling to one side, reaching out and grabbing things... and best of all, LAUGHING! Rather than a giggle, Callum's laugh is sort of a "heh-heh-heh" as if he's surprised to be laughing.
By way of comparison, Anya's first turn in the Jolly Jumper was at 5 months, so Callum seems to be developing physically a lot more quickly. It's amazing to watch him try so hard to sit up -- cranes his neck and lifts his head. Anya only sat up after months and months of being carried around upright and never seemed to be trying to sit up by herself.
On the other hand, Anya was already reaching out and grabbing things at 12 weeks old (Callum is now 16 weeks) so she was ahead in other ways. My hairdresser (who has 4 kids) said she thinks boys are lazier and don't develop as quickly! Funny, as general consensus seems to be that boys are usually ahead of girls in physical skills.
I've also been reading about birth order (Time Magazine) -- apparently we can expect Anya to be more intelligent/ambitious, conformist/conservative and serious, while Callum will most likely be more agreeable, rebellious and humorous. Firstborns are also usually physically larger, but so far that's not the case! I was interested to read that elder siblings' intelligence is boosted by the tutor effect -- having to explain things to their younger siblings.