All the ducks below are from the same parents and hatch but some are clearly bigger. The 2 little ones had a hard hatch and I chucked it up to them be

[Ducks4u]

 

[Ducks4u]

Uncertain if the two little ones are runts or perhaps the 3 large ones are jumbos.
Dad is a jumbo peeking mom is a regular size peeking.

 

[Isaac 0]

Looks like two may have more of mom's side.

 

[Ducks4u]

Looks like two may have more of mom's side.

We are thinking:

Jumbo Dad genetically must be Jj ( J= Jumbo / j=regular size)

Mom genetically- jj

3 babies - Jj
2 babies - jj