Linzer I also just found out that some friends are expecting dc3. Hopefully I'll be able to find out whether it was planned they already have one of each so it can't be, can it? I dream of having four, but mostly of how lovely it would be to have frequent visits when they've all grown up and less of the driving them to zillions of afterschool activities, refereeing fights, etc. In any case, atm I'd be happy to be able to produce no. 2 .
Canella very impressed with your fleißig shredding. I'm another one who's half tempted to try it, but I've got too many other things that I'm failing to make time to do.
gator just to go back to the sitting thing - I bet half the mums at that course were thinking "oh, my dc loves to do that, too, I'm so glad that British woman is getting told off and not me!" Certainly everyone in my baby group used to do it and we all went to PEKiP, which is ridiculously anti-sitting. It is, in fact, a PEKiP exercise anyway, our instructor told us to make sure the baby is doing as much of the work as possible itself, ie. he should hold onto one of your fingers on each side, rather than you grabbing his wrists, and his head should be coming up first. In the PEKiP version you lower them back down without letting them spend any time in a sitting position, of course 
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Re highchair sitting to eat, the paediatrician told me (without me asking, I hasten to add) that it was okay to sit a 6mo in a highchair supported by cushions for up to 1/2 an hour. The position with legs dangling apparently puts less stress on the back than sitting on the floor (this at least makes sense).
I think it's all based on a concern that babies should not skip stages in their motor development. So they should roll back to front, front to back, push up onto all fours, sit themselves up, crawl, pull up to standing, stand with their feet flat on the floor, cruise, walk, etc. Some babies do things in a slightly different order, but it's important they are doing everything themselves and that they do all stages. What exactly might go wrong if they don't is not always made clear. Tbh I've been brainwashed enough to think that it's not an altogether bad attitude. It certainly counteracts the natural parenting instinct to worry about child X doing something that mine can't yet and it reduces accidents (I once failed to prevent a friend's 5mo toppling over forwards from sitting and cracking his head on the wooden toy he was trying to reach - felt terrible about it for weeks).
But if you're still worried, go to Behaviour/Development and count how many pages it takes before you find the first thread titled "Help! 6mo not sitting yet" 
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