The toddler years involve more than just baby-proofing, sippy cups and potty training. Children at this stage, which occurs between 1 and 3 years old, go through important physical, mental and social changes. There are a few general milestones that will help you track how your toddler is developing. Remember, all kids develop at different rates, so don't go comparing your toddler to her little buddies.
12 to 18 months
It's both exciting and nerve-racking when your child starts walking--he'll gain a lot more independence, but now you'll have to watch him like a hawk. He'll initially develop this skill when he's around 12 months old by picking himself up, cruising around furniture and taking his first steps. By the time he's 14 to 16 months old, he'll likely be able to stand on his own and walk well.
Another huge milestone will be his ability to communicate with you, such as indicating a desire by pointing or being able to follow a simple command. Much of what he'll first say or do might involve imitating you, especially if you're intentional about showing him how you drink from a cup or manipulate crayons to color. By 18 months he'll be able to recognize you as someone he can turn to for help--and he'll be able to communicate it a lot better than he did in the newborn days (read: not screaming like a banshee).
18 to 24 months
Just because you put two toddlers next to each other doesn't mean they're going to get along. Play is extremely important to toddlers who are nearing two years old, but don't worry if your child isn't super interactive with others at this age, since this stage involves becoming more independent. She may simply be focused on her own routine and perspective and not yet understand how to incorporate others into her interests.
The trade-off is that you can use this time to teach skills that will be useful for interactive play later. When your child is between 18 to 24 months, she should generally be able to throw a ball overhand and kick a ball forward. She won't be able to fully understand the concept of time, so any game you play will need a routine filled with benchmarks to indicate when the activity begins and ends.
24 to 30 months
Ah, the terrible twos. This stage actually may be nothing more than your toddler discovering that he has an opinion and wants it heard, and kids struggle throughout childhood with their independence clashing with boundaries. The difference at this stage is your little one may throw a tantrum that's less about rebellion and more about frustration or exhaustion. One of the best things you can do is communicate that you heard him, even if you can't grant his request. Help him shift gears by allowing him time to express himself and calm down before you move him onto the next activity.
Another change you'll note involves his eating habits, such as developing favorite foods while still wanting to try new foods. He'll likely start sampling the food off your plate as well as eating his own--hopefully by asking first.
30 to 36 months
An older toddler will usually have the routine and expectations you have for her down pat. She'll also notice any differences in how you parent her versus other siblings, such as offering snacks before dinner or getting extra playtime. Toddlers have a keen sense of justice (to put it mildly), so the more consistent you keep things, the calmer they'll stay.
This stage can be somewhat bittersweet as you watch your little one start to do more complex things on her own. The gross motor skills she's developed up to this point will allow her to ride a tricycle or stand briefly on one foot; however, with all this new activity, don't expect that naps will still be needed as long or as frequently. The upside is she'll become more imaginative in how she plays--and more interactive with others.