Is stretching baby bunny normal??

Hello everyone!

Our doe gave birth to a litter of four last week, two of which were delayed and dead since birth.

The two surviving kits seems healthy and normal, one was significantly outgrowing the other though.

This morning I found the smaller one out of the nesting box cold and shivering. I warmed it up and realised it had a flat belly.

I picked up the doe and fed the kit a bit. After that the kit seemed to have got back to normal apart from the stretches its doing!

Is it normal for them to do this?? Its our first time having baby bunnies so we really don't know too much.

Also, the nesting box has became really dirty and smelly. We are planning on cleaning it out and replace it with a smaller one since the kits are now one week old. Would there be any problem to this?

Thanks everyone!