Coordinating events as precise as births in a multiplanetary society is already going to be inherently impractical. The family back home should celebrate when

Coordinating events as precise as births in a multiplanetary society is already going to be inherently impractical. The family back home should celebrate when it's relevant. If there's a wormhole, then the kid can probably make a call through it, so they can call on their (self-perceived) birthday. If the wormhole is a one-way trip, then the people back home should wait an additional 4.3 years to celebrate, because they won't have any idea until then.