Rehoming/selling axolotl babies - how old?

[legnadesufnoc]

We had a surprise clutch of eggs recently that we have carefully looked after and have some beautiful, healthy babies. My question is, at what age/size is it suitable to sell/rehome them? I can see their back legs starting to come through, so I know it's still early yet, but would love to know when it is suitable. Also, what is the best way to package them for sending?
Thanks