Angels can fail because God allows them to make decisions and they are lesser beings than the perfect God. They can go astray, but the task is legitimate. God never tells they aren't allowed to instruct people - "just shut up and babysit them".
I don't really have time [to babysit my twin cousins]. And, well, I actually have my own babysitter sometimes.
When you have somebody who takes their craft seriously, you don't have to babysit them and be there all the time.
Anyone who still supports George Bush would still let Michael Jackson babysit their kids.