This past weekend — at just shy of 9 months of age — Aerin finally sprouted her first two teeth.

As I proudly ran my finger over Aerin’s new incisors (and got repeatedly bitten in the process, as having her mother’s finger shoved in her mouth is something that she obviously does not like), I couldn’t help but think back to when Claire got her first teeth at 6 months of age. I had expected Aerin to get her first teeth at approximately the same age too, so the 3-month difference — which is quite large in a baby time — was yet another evidence of how differently my daughters grow, develop, and become themselves.

One of the things I find most difficult about parenthood is resisting the urge to compare the two. Who did _____ first? Who is more/less _____ than the other? Who is better/worse at _____ than the other?

After all, I have always hated it when my parents compared me to my sister, or even other kids while growing up. Isn’t this is a common complaint among many children? Parents should respect the fact that all kids grow at different paces, and develop different tastes and aptitudes along the way…right?

But it is so difficult not to. It practically seems like second nature to measure Aerin alongside her older sister because Claire, my firstborn, is what I currently know most intimately about raising a child. And I assume that as they grow older, I will start comparing Claire to Aerin as well.

In the past few weeks, Aerin has started to crawl…backwards.

For instance, we already know that Claire generally seems to a more detail-oriented person, while Aerin is more interested in the big picture. I had first suspected this when Aerin started to master her gross motor skills much faster than Claire, who in contrast always stayed ahead of the curve in her fine motor skills but lagged slightly behind in her gross motor skills. And now that Aerin’s personality is surfacing more, this becomes more and more apparent when you observe how each girl plays and interacts with the world around them.

We also know that Claire is much more cautious and afraid of new experiences. Aerin, on the other hand, seems fearless and always seems to want to explore, touch, taste, and feel everything around her. We never really had to worry too much about Claire’s safety while she learned to become more mobile, because she has always been such a cautious and careful little girl. But now that Aerin is crawling (another difference: Claire never crawled), we really need to keep a careful eye on her and even baby-proof the house much further than we did with Claire.

Aerin is already more personable and sociable than Claire. Claire is much more sensitive and observant. Claire’s concentration levels have always been very high for her age, while Aerin is easily distracted like other babies. The list goes on and on.

Claire’s very first knee scrape occurred when she was 21 months old.

I know that there’s a good chance my daughters’ personalities will change as they continue to age and mature. But for the moment — at 22 months and 9 months of age — they are as different as night and day. And while many people remark on their difference in personalities, it is so much more apparent to me, their mother.

It is now clear to me that I cannot help but compare my children to each other. As a result, the best way to approach this would be to acknowledge and embrace each girls’ differences, and try my best not to pressure them to be something they are not, or something they would be unhappy with.

And never, ever, start a sentence with “Why can’t you be more like…”