Welcome to the world of cloth! I too didn't discover modern cloth nappies until I had my second baby and felt 'if only I'd known!!!' too
I second what the others have said about buying a couple of different types of nappies to try out as everyone seems to have a different favourite. I haven't used cloth on a newborn (my son was 5mths old when we switched from disposables) but brands that I've tried & would recommend are:
Fuzzi Bunz (probably small for your daughter and medium or large for your son, depending on his size),
Honeychild (try medium on both - although my 13kg 23mth old wears a large),
BumGenius V3 one-size (you'll probably need both inserts for your son and possibly the bigger size insert for your daughter as the 'newborn' insert is really only the size of a booster)
Itti Bitti D'lish (possibly medium for your daughter and large for your son. I can't vouch for poo containment on a newborn but they would be a lovely trim option on your son)
Foxybots (small for your daughter & large for your son - they're gorgeous fabrics with generous pockets for stuffing, esp overnight).
Have fun shopping and don't hesitate to pop back on here for advice if you have any problems - we love talking about nappies
Vic xx