Perhaps someone else on our team may have a better grasp of the canon law with respect to this issue, but my sense is that there is no harm, in fact it may help to bond your family provided there is no underlying attempt to co-opt the child's formation.
This matter will require your discernment.
- What do you read as your parent's ultimate motive?
- What is their attitude toward Catholicism?
If you have any reservations due to concerns that they may be overstepping their role, than you could say, No.
So, in short:
- if they want to celebrate this child as a child of God
- bless her, and
- throw a party
- If they are anti-Catholic
- have their own agenda, and
- may try and subvert her Catholic upbringing in any way, shape, or form