I'm sure you were going for a totally clean background but it looks like you've got the juice on the fill light set way too high?
See your little girl? She has no shadows at all so her outline doesn't possess depth, it looks like she was pasted in after the event. The highlight could do with being turned down a touch too, the light has bled into both heads on your boys, the fella on the left looks like his ears are not attached.
They look great kids by the way, you should be proud of them.