Why is “A” needed?

Question

A Manuel se le ha muerto el perro y el pobre está muy afectado.Why does sentence need A at the beginning? (The other examples don’t have it). Thanks very muchShirley

Accepted Answer

Hola Shirley
What we are using is an indirect object pronoun. This pronoun, which in "A Manuel se le ha muerto el perro" is "le, can be repeated by another indirect object referring to the actual person if we are naming them: "A Manuel". We always need the A + person" in this case. 
The other sentences that we are using with other "dativos" are not being specific about who, because it is clear from just seeing the short pronoun (nos, me) so we are not using that extra indirect object, but we could also use it, for example:

A nosotros, los niños se nos están haciendo mayores sin darnos cuenta.
Our children are growing without us realising.
A mí, mi hija pequeña no me come nada y estoy muy preocupada.
My younger daughter doesn't eat anything and I am very worried.

I hope this clarifies it.
Saludos
Inma