Here is a list of adoption-themed movies that you could watch with your kids. I recommend watching them first to pre-empt potential questions.

Rating G ( general) Date
Meet the Robinsons 2007
The Tigger Movie 2000
Rated PG
Annie 2014
Big Hero 6 2014
The Boxtrolls 2014
Despicable Me 2010
Despicable Me 2 2013
Earth to Echo 2014
Finding Dory 2016
Frozen 2013
Kung Fu Panda 2008
Kung Fu Panda 2 2011
Kung Fu Panda 3 2016
Lilo and Stitch 2002
Mr. Peabody & Sherman 2014
Paddington 2014
Creed 2015
Man of Steel 2013
Teenage Mutant Ninja Turtles 2014