Question: Axolotl eating plants

One of my axolotls has started eating leaves in addition to their daily food.They were born in May and I alternate daily between feeding them frozen blood worms and a 50/50 brine shrimp mix. Both of my lotls eat about the same amount and have never had any problems with fighting over food. Is this a sign of deficiency, boredom maybe, or am I worrying over nothing? Has anyone had any experience with this and can offer any advice?
addendum: they have very fine sand in their aquarium and Luka tends to eat some of the sand although the leaves are new. Should I also be concerned about the sand, I have heard that it helps with digestion but just want to make sure.

I would start feeding them earthworms now, cut to size if needed.
With regards to sand, you may find as your axolotl is trying to eat the smaller food, it is gulping in sand at the same time. The sand should pass through OK.
The same may apply to the leaves, maybe it can small some pieces of food on the leaves and is trying to eat it? Is there water movement that is making the leaves move? it is possible it is thinking the moving leaves are live food.
Finally ( I get there in the end) I did have a couple of adult axolotl that would eat the duck weed. They were well fed earthworm, which would sink, but at random times of the day I would see them munching away. It appeared intentional and I never found a logical reason why. It certainly passed through their bodies as the poop would contain the undigested evidence.