I know you'll have some posters who say that they have had low energy and yet others who have felt and continue to feel great, but
you have to expect that the responses you get here are going to be anecdotal. You, personally, are only going to feel as good as your (vegan) diet will be
I think that no matter what you eat or which diet you follow: excellent overall nutrition (other health and exercise factors aside) = good energy.
So, that aside, I have been vegan for 7 years now - through nursing two kids (and part of that tandem) and 1 pregnancy. Dh (also vegan of 7 years) and the two kiddos also have no energy problems. But our diets are really good: organically grown, seasonal whole foods, cooking and baking from scratch, soy and sugar in moderation, lots of good water (and other liquids - not carrot juice, lol!), supplements and a careful eye on omega-3 and -6's.
ETA: my kids are definitely not neurologically-impaired. On the contrary, both my children are seriously smart cookies - my ds is considered gifted
Michelle in NY