Toddlers have some very clear ideas about their world. They want what they want when they want it, and they will let you know in no uncertain terms if they are unhappy with your response. And when they want to nurse, you'll know about it.
Toddlers are not newborns. They don't need to nurse on demand. They can eat solid foods, drink from a cup, and feed themselves (messily, to be sure). GI can be just as happy sitting in his high chair with some finger foods as cuddled in my arms nursing. Well, almost as happy. If he's hungry, though, food will suffice for him if it's not a good time to nurse him, or if I just don't feel like it. The only time it's nurse or bust is when he's tired and wants to fall asleep, and then I'll lay down with him in bed and let him nurse until he drifts off. Sometimes it's even that simple.
Toddlers are little people whose brains are developing at an incredible rate. One of the things they start learning is the difference between need and want. At the same time, they're learning to understand an incredible number of words. You'll notice your little one start to be able to follow directions, identify body parts, look at named people, point to pictures of objects and animals you name, and so on. This is called "receptive" language, and it develops much more quickly and earlier than "expressive" language. Expressive language is talking. A baby and toddler can understand an instruction or word much earlier than he can say it. This is frustrating, because he wants to tell you something, knows there's a way to do it, but can't make his mouth cooperate.
This is where teaching him some simple signs or syllables to express his need can be very powerful. When a baby or toddler can ask for what he wants and know that you understand his desire, his frustration evaporates. When a toddler can express his need, both of you can be on the same page. Pick a few basic expressions for your toddler to use first. I imagine "nurse" or "breastfeed" will be high on the list of frequently-requested items. I recommend the following three words: nurse, eat, and more. Those three words seem to satisfy most of my toddlers' basic requests.
So, when GI started trying to pull my shirt off whenever he wanted to nurse, I knew it was time to really start to work with him on using a hand sign or word instead. I had been trying to teach him the ASL word for "more," which is a simple sign that most toddlers can manage some form of. It looks like this: