The United Nations response to

the situation in Madaya has been criticised in more than one place - and sometimes by people who should know better.
It's a horrifying situation - far worse than the media is suggesting. The  UN is being criticised for being "too slow" to respond and responding in the "wrong" way. 
These criticisms show a lack of understanding about the way in which the UN works - or doesn't work.  It also shows a lack of understanding about just what the UN can do.
People tend to believe the UN can do whatever it wants. They tend to believe the UN can make a decision and then people must act on it. 
It doesn't work like that. The UN is individual nations sometimes working together, sometimes not. On occasions they will meet and negotiate. They might ask for help or offer it.  It all has to be negotiated. Other countries can't just say, "We are coming in to deliver food and medical supplies."
The people in Madaya are hostages. Their release has to be negotiated. Those who hold them are not going to let go just because the UN says they must, or even if they ask nicely. It won't happen.
Madaya is in a war zone. It's dangerous. People get killed there. They die there. Those using them as hostages don't care about them. They only care about how they can use them to get what they want. 
Those taking aid in are risking their lives. Put a foot in the wrong place  and they could step on a landmine that will blow the entire situation apart - aid workers included. 
As for the sort of aid being delivered. Well, that had to negotiated too. You can't just take in anything. You can only take in what the  hostage takers are willing to allow - and what others are willing to provide. If the hostage takers said "rice" then it will be "rice" but if they said "flour" then it would have to be flour. It would be no good telling them "rice was not available". 
Someone said, "Why not just take everyone out and put them in a refugee camp over the border?" It's not going to happen.That wouldn't leave the rebels anyone  to negotiate with would it?
I have, after many years of association with the UN, my doubts about the way it works and just how effective it is. But, it is better than nothing and at least a little food has reached the people of Madaya. There are other places also in urgent need of help and it is by no means the only conflict zone in the world or the only place in urgent need of assistance. I know we can't do everything for everyone and money won't solve all problems.
As a refugee once said to me, "Hug your family and say something nice to a stranger. It helps."