Etiquette Question - wedding invites

Greetings folks:

Just wanting to get some opinions from out there. We've been invited to
a wedding, which it will cost a fair bit for us to go to; car rental,
gas, clothing for me, wedding gift, etc.

Anyhow, we just learned that our five month old isn't welcome at the
reception, not even for just the dinner portion. The baby is
exclusively breastfed, not like I could just leave him with someone.
Even if he weren't, everyone I know in the area will be at the wedding,
there's no one to leave him with.

Question is, is this the norm for weddings? When I got married this
didn't even cross my mind, and I confess it didn't even occur to me
that DS wouldn't be welcome when we got the invite. I always thought
that weddings were a family celebration, and families do include
children. I can't see us spending all this cash to go, when the most
important member of my family isn't welcome.

What do you all think?

KD & G