Is this a swaddle or a sleep sack?

No. It is a blanket, so it is draped or tucked rather than worn. For safe sleep, follow AAP guidance and keep loose blankets out of the crib for infants.

Can I use it in a car seat?

It is sold as a car essential, so it is meant for covering a baby in the seat. Do not route it under or through the harness; the straps should sit flat against the child.

The material and care instructions are not specified in the product information. Check the label on arrival before washing.

What size is the blanket?

The dimensions are not listed. Treat it as a light stroller or car-seat cover rather than a full crib blanket until you confirm the size.

Is it an official Little Einsteins product?

The listing names the Little Einsteins theme but does not state a license. If official merchandise matters to you, confirm with the seller before buying.