Compacts are convenient outdoor but indoors/poor light and action (as in kids not keeping still)... its a bit more tricky. In pure pixel peep terms, ISO400 on compact is like close to ISO3200 on your 550D

Also consider the shutterlag is considerably worst on compacts.
If cost is a major issue to you and you won't be spending money like water on lens --> NEX5 or better still the NEX5N with better color jpegs.
600D if you want swivelling screen (good for low angles and video)
550D if you wanna save that couple hundred linggit. Both shoots the same.
Strictly speaking, NEX-5N is still considerably slower than a 550D in terms of operation speed and AF

and...
550D + 18-55mm kitlens = 530grams + 200grams = 730grams
NEX-5 + 18-55mm kitlens = 288grams + 194grams = 482grams
= Difference 248grams
a can of coca cola weight 390grams.

IMHO opinion... primary different is the feel when shooting. With a DSLR like the 600D, the view through the viewfinder is like seeing the world through a small window while on the EVF equipped A55, it's like seeing the world through a small LCD screen.