..keep them simple!
I would begin with simple signs and signs/words that actually MEAN things to them in their daily life and activities.. ie..
- more, for more food
- milk, for bottle or nursing
- all done, for letting you know they are full
- mom, duh :)
- dad, to be kind.. hehe jk!
- please, start teaching manners
- thank you, same as above
- cookie, which could mean snack like food
- tired or sleepy, signs they want to go to bed!