Are they eating hay well? Are they gaining weight? This is vital - hay is the most important part of the diet and if they are losing weight then their hay intake has reduced.
Are they bored of their veg and need some more variety?
We can’t know if there is something wrong with them, but if hay intake has also reduced and they are losing weight then you need to step in.
If they are eating hay and gaining weight well, then they may just be being fussy over their veg and in that case, I’d add some variety, switch things up, keep an eye on them, but don’t be too concerned.
Otherwise, please do see a vet.