For toddlers, there are many ways for learning to occur, and for many it will not happen in a structured classroom learning environment as they are simply too young to thrive through such methods.
However, a common learning approach for this age group is play based learning, and this is a great tactic for incorporating learning through every day play that your toddlers will already be engaging in. Learning or improving awareness of the alphabet can easily be achieved through play and through the natural events in a family day. Here are some ideas if you're seeking inspiration:
1) Games There are tonnes of games that are purpose-made for alphabet learning, such as alphabet cards, memory cards or puzzles that piece together to form words or associations. However, any games can be overlayed with some alphabet association through just talking about what you are doing. For example, a game of Tumbling Monkeys (or Barrel of Monkeys) can be played with the adult making reference to the spelling of the playing components, "Ok, it's your turn to put the banana on the tree, the word banana starts with the letter B, so that's B for banana". You can do the same for many of the games out there.
2) Signs My son is three now, so without prompting he now enjoys telling me whenever he can see the letter his name starts with. His name starts with the letter X so handily, almost everywhere we seem to go there is an exit sign, which he happily points out has the letter X in. However, you can look out for signs everywhere you go, from supermarkets, to road signs, billboards and signs in the park. See if you can get your child to identify a letter to you. A bit like eye spy, you can say, "I can see the letter T - can you see it anywhere?" Once you've played this a few times, it becomes something kids will do almost every time you're out.
3) Books In addition to reading to your child, you can also spell out certain words, or let them know what certain characters names begin with. So if the book you are reading has a dinosaur called Pete in the book then let them know that Pete starts with the letter P and show them the letter. Over time, you'll get to full word recognition. Books with large bold print will assist you here. There are also numerous books solely designed to help your child learn and recognise the letters of the alphabet.
4) Singing Obviously the song that springs to mind here is the alphabet song, where kids will learn to sing the full range of A-Z, but there are other songs where certain words will be spelled out. The song about Bingo the Dog (B-I-N-G-O) is a good one, but you can also just choose a song that starts with a letter you are focusing on. E.g. Twinkle Twinkle little star for the letter T.
5) Colouring If you google "colouring in printables" on the internet, you can find hundreds of free printing resources for your kids to colour in. Simply go to the site and then print them off. Your kids will have fun colouring in the picture that is associated with a particular letter.
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6) Bath crayons Tub time is fun time, and bath crayons mean that your kids can doodle all over the bath whilst they soak in the suds. We bought a pack of cheap and cheerful crayons from Kmart for $1 and they are fantastic for practising drawing letters and shapes. Best of all it all washes off when you are done.
7) Alphabet fridge magnets Place some alphabet fridge magnets on the fridge and suddenly you'll have a little one asking you what each letter is. Then you can progress to having fun making up words together. It's great for spelling, for letter awareness and also for keeping little ones busy whilst you are cleaning or cooking in the kitchen.
8) Alphabet Cooking Many kids love to help out in the kitchen, so cooking things in the shape of the alphabet letters is a great way to enhance the learning of the ABC's. Cheap cookie cutters can be purchased online, and kids can help with cutting them out and decorating them. If you don't have cutters, the icing letters onto cup cakes can be a great learning experience. This also works well with learning your colours.
Toys There are loads of toys available that are purpose made for learning the alphabet. Lots of these are aimed from babies upwards, and can include letter identification and even spelling games; so plenty of choice for all ages.
10) Alphabet Flashcards There are lots of ways to use flashcards to enhance learning, and you can make lots of games with the cards so that it's not just the rote learning type experience. You could grab 5 cards at a time, lay them out in front of your child, get them to spell out the letters. Then ask your child to close their eyes, and hide one of the letters. When your child opens their eyes, ask them which letter is missing.
Before you know it, you and your child will be singing the alphabet song in your respective sleeps.