Apple's instructions on how to do this (for a child under 13) are in the support document Move a child to another group using Family Sharing. Be aware that the document it written for the purpose of the current owner of the family group with the child as a member, and not from your perspective of the owner of the family group inviting a child to join. Where it says "your" and "you" it means, in your situation, your husband.
The process does, however, require you to use a device signed into your husband's iCloud account so you will need to know the password for that device to open it up for you to use.
The summary version of the instructions is that you invite your child to join your family sharing group and your husband's device approves this transfer.
This is another process you could do without at this sad time for you but it should be an uncomplicated transfer.