afterthought

[silly moo]

Another one on the same lines.
A child born after a long gap is often called an afterthought, in the US he / she is often called a tag along .
ANy other suggestions?

[Woodstock]

My Mum and Dad called me a complete mistake!

[Kingaroo]

I've heard "caboose" especially when trailing after several older siblings.

[spudqueen]

A Bonus

[silly moo]

I like 'a bonus'
must make you feel special!

[smudge]

An enhancement!

[thikasabrik]

For Royalty, it is usually an heir and a spare.

When I look at my youngest, I often think "he seemed like a good idea at the time..."

[Ouisch]

Surprise

Change-of-Life Baby

Last Ditch Tax Exemption.

[tpfan]

In N. I. it's often called "a wee late one";

for shotgun wedding the cause would be "a wee early one"

[tpfan]

oh, just remembered Leon Urris' definition in  "Trinity"

"the scrapings of the pot"

[ALLO]

i would say oooooooppppppppppsssssssss!!!!!!!!11

and uhoh!!!!!!!!