Happy half-birthday, baby True! Khloe Kardashian shared the cutest pic of a "cousin cupcake" party she threw for her daughter's six-month birthday with Saint, Stormi, Chicago, and Dream. She captioned it "Cousin Cupcake Party!!! Keeping Up With The Kousins"

Kim Kardashian posted her own tribute -- a photo of daughter North playing with little True, showing her how an activity cube works. She captioned it "Cousin Love."

The milestone comes at a time when True's parents appear to be having trouble in their relationship ... a source tells >People magazine, "Khloé is stable, content and very happy with being a mom and with how things are going with True ... As for Tristan, things are still quite up in the air between them. Things seem more unstable in the relationship right now."

It's been six months since Tristan was caught cheating on Khloe, days before the birth of their daughter and while Thompson has "been trying," according to the source, Khloe posted some cryptic messages on social media recently, hinting that there may be trouble. Sources say Khloe has put her plans to move back to Cleveland with baby True on hold ...

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Cousin Love 💕

A post shared by Kim Kardashian West (@kimkardashian) on