1 definition by marshmallowobsessed

Top Definition
The kid of the person you are dating that quickly becomes almost your own because you spend so much time with them outside of your dating relationship.
I am in beginning stages of dating a man with a child and I also have a child. When I go anywhere with my child it is "expected" that my instakid (the son or daughter of my boyfriend) will also join us.
by marshmallowobsessed March 26, 2013
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