Young wood pigeon just sitting there


I am concerned about a young wood pigeon in my garden, it cannot fly but doesn't seem to be trying, it just sits there.

There were originally two which appeared in my garden on Wednesday (it's now Sunday). I didn't take much notice of them but in the evening we noticed one of them was still there.  It was dark and we thought it was ill so I put it in a box in the garage overnight.

Next morning let it out and its sibling appeared from where it had been hiding.  I phoned a wildlife centre who identified it from my description as a young wood pigeon and said that they stay on the ground for a few days until they can fly.  So I left them to it and did not put them in the garage on Thursday night, and they hid behind the bin when it got dark.  

The next morning one of them had been killed by a cat.  It didn't eat it, just killed it.  So now I put the remaining one in the garage at night.  I'll do that till it can fly off.  The parent comes and stays with it during the day, when the parent disappears I push the chick into the box and put it in the garage with food and some bird seed.

My problem is that the young bird is just sitting there during the day.  I am not sure if / what it is eating, though it does seem to be producing poo.  And it doesn't seem to be practising flying at all.  When I opened the garage this morning, it was reluctant to come out.  I don't want the parent to be put off, so in the end I gently pushed it outside.  It then seemed to want to go in the kitchen.  I gently herded it to the back of the house where the parent could see it.

Is is normal for it to just sit there, not trying to fly?