Hi...you have some cutie pies! According to the "breed standard" by the Yorkshire Terrier Club of America website.
Yorkshire Terrier Club of America, the white spot on the chest is normal if it doesn't exceed 1".

Donna
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I'm Donna. DH is Mike, son is Grant &

is Gunnar
WE all

Gunnar Lee

. 7.9Lbs of lovable Terror