When you are sure that your baby knows a sign and doesn’t use it, it’s time to insist that they do. This usually happens when your baby whines, reaches and grunts, while looking at an object and to you and yet they’ve successfully used the sign for it previously. Unfortunately, this means that your baby is still holding rudimentary communication patterns, however, these can be fixed with some diligence on your part.
First, always stop yourself from giving into whining. Instead you’re going to want to reinforce communication instead. Next, just talk your baby through. Ask them what it is they want and ask them to “use their signs.” If you know full well what they want, just ask them to produce the sign first, before giving it to them. You can say “I know you want milk, but you must first do the sign for milk.” In this case, I would hesitate in doing the sign for milk, but this depends, ultimately, on your goal. If it’s to reduce whining and you know for certain that they can do with sign, then give them plenty of opportunity to come up with the sign independently themselves. To reduce signing, you need your baby to come up with the words themselves instead of just copying you. If you are happy to have your baby simply do the sign, then by all means model the sign yourself.
Ultimately you want your baby to strengthen the neural pathways required to replace whining with signing, and in the long run teach your baby the difference between using poor communication patterns, and appropriate ones. If at first your baby won’t sign their wants, ask them in a few different ways. You might even point to the object or lift it up as you prompt your baby for the sign. Never just give into whining on its own, even you’re required to modeling the sign for them, or helping your baby do it by moving their hands
Advice: It’s a good practice to always give into new signs so as to encourage proper communication. You’ll also want to give in to existing signs on occasion even if you aren’t in the mood, so as to reinforce proper requesting. However, you should never follow a baby’s whining with positive outcomes.