Potty training isn't going to be easy for most toddlers no matter what you do, but as a mom, I agree that potty training a second child is actually easier. My first toddler potty trained around age three, which is about normal for boys, while his little brother, now barely over age two, is already almost there. I certainly wouldn't suggest having more than one child just to make potty training easier, but it's a nice little perk.
Why are second children easier to potty train?
In my experience, it was because the second child had someone he related to better to watch. His brother even chose to teach him things like to hold his pee-pee down so that pee went into the toilet, and to flush after. It wasn't an alien thing he was the only kid doing; it was just another thing he learned from his sibling. I'd imagine the effectiveness of having an older sibling help potty train the younger would, however, be less effective if your children were not the same gender.
How can you use it?
I quickly realized the power of siblings and made efforts to maximize the opportunity. For example, since both boys wanted a treat if one used the potty, I'd give the older sibling a treat if he helped his brother use the potty as well even if it was something as simple as telling him he did a great job when he was done. This kept both boys happy and encouraged the older toddler to keep leading the younger into diaper freedom. If your older child is not interested in helping, just let the young observe like he/she does to learn from you. There must be some inborn desire to be just like our older siblings, because it works every time.
Are there any disadvantages?
While having an older child to help a younger toddler potty train is awesome, you have to be careful not to turn it into a be-like-big-brother/sister situation. Be sure to still make it a celebration of individual growth. For instance, we still let our second toddler go pick out new undies despite having plenty of hand-me-downs from his brother that fit and we still let him pick his own potty chair. We also avoided saying things like, "Do you want to be big like brother?" or "Brother does it, you can too!" You don't want to set your children up for rivalry or make the younger feel like he or she is always following in his or her sibling's shadow.
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