I'm in a similar situation - we've been big meat eaters forever and I switched us all to vegan overnight almost a month ago. We did have one or two meat free days a week though, but still that involved dairy. The kids think it's great, although my son eats meat when he goes to his father's house alternate weekends. I'm not forcing them, just leading by example.
With regard to the newborn, if you are obtaining all the right nutrition your breast milk will be ample, as I'm sure you know. Omega 3 and B12 are vital to that though. As for weaning, I didn't give it much thought until the other day but my kids were all vegan weaned anyway! I dd the usual steamed carrot, apple, fruit purees, veg purees, then went into rice an veg etc. I'm sure someone will be along soon to tell you more about baby and toddler vegan issues, but I'm just saying it's possible, don't worry.
We only discovered Flax/Linseed this week. I opened the packet to put some on my porridge this morning and dropped it - all in my two year old granndaughters bowl, my son's and mine. I scraped off what could be rescued and stirred the rest in. Kids didn't even notice!
I take a supplement for vegans - although I don't think it's really that necessary at the moment. I'm sure my B12 stores are sufficient as I'm newly vegan, as opposed to longer standing vegans, but it eases my mind somewhat. And it doesn't hurt to take it.
Mostly I have had so much fun cooking! I've not made one disaster yet and we've been eating some great foods. Quinoa was a revelation to us, is a superfood and very versatile. Although we ate fresh food before, I did buy white rice and white bread for the kids - now they are on brown rice and wholemeal only. If you need meal ideas, VEGWEB
is a great site.
I add fruit to the cereals in the morning, my son has gone from taking ham sandwiches to school with crisps, chocolate cake, fruit shoot drink and cheese strings to today's effort, which was a wholemeal sandwich with mushroom paté, banana, apple, and a tub of cashews, wasabi peas and chilli rice crackers and a bottle of water. Incidentally, he is calmer and has far more concentration than before! and he prefers Agave nectar to honey any day.
Good luck with it, if you want to ask any more questions please do! xxx
editted to add: I forgot to say, a wise person on these boards told me somewhere not to think of vegan substitutes, but vegan alternatives. It helps you to not expect everything to taste like meat, and I haven't missed meat at all since being vegan.