This is a moment as comes up only that once - and you captured it.
The bright hand in the foreground is not only a little distracting, but I see that you had little influence over how this scene would develop and you captured them with these funny expressions that make everyone smile ... I like that.
Sadly with twins these little 'moments ' come up too often! You dont think it needs a crop? My problemn is, the only critique I have is my husband who is biased for two main reasons, 1) His wife is taking the picture 2) his kids are the subjects!
So I need some unbiased, even 'cruel to be kind' advice/opinions
With this one you cannot crop out the hand, the crop you get would be too close, you'd even have to crop into their chins.
When these moments come up often, as you say, the best suggestion would be: be on the alert with the camera ready and wait for more moments of the kind. There will be one with no brightly lit (by the on-camera flash?) hand in the foreground. Be on the lurk and shoot - with the CAMERA only, of course!?!?!?