Pros
Does great work at a scale that incomparable (helps hundreds of millions of children), despite some inefficiencies. Great salary and benefits - IF YOU'RE ONE A FULL TIME CONTRACT. Massive inequality between contract types (especially between senior staff members, who have a very cushy existence...to younger people who are often on "consultancies" with zero benefits.
Cons
Many of the staff are selfish and nepotistic - care more about themselves and promotion that the children they're supposed to be helping. The culture is almost corporate and vey much "dog eat dog". A lot of crazy people work there - especially ones that have "been in the field" for too long, and as a result, many of the senior staff have severe personality disorders. And they take this out on many younger staff - especially ones who are enthusiastic about the cause and want to make a difference. The idealists don't last long as a result.