The biggest money mistake parents make before having their first child

Having a baby fundamentally changes parents' lifestyles, from how they spend their time to how they think about the future.

Starting a family also means $4, from doctor's visits and hospital bills to loading up on all the gear a new baby needs.

But many parents get caught up in the excitement and adorableness of baby items and end up purchasing far too many things that they don't actually need. The biggest mistake: stocking up on too many baby clothes.

"It's so fun to buy for kids! I love buying for kids!" Pam Horack, CFP and $4, told Business Insider. "Everything is so cute and it's so easy to buy for them because they're just adorable. But then they're done with that in six months. That stuff goes super quick."

At around $8 a pop for a tiny dress or teensy pair of overalls, baby clothes can be relatively cheap, making them seem like an innocuous expense. What could it hurt picking up a couple more onesies? Can always use more!

But those small price tags add up quickly. Not to mention, babies graduate to new clothing sizes every month or so.

"We seem to go through his clothes constantly," Anna Newell Jones from $4 $4 of her then 5-month-old son. "Just as soon as we pull out a new size of clothes we're putting others away, and he doesn't even wear most of the items!"

Between baby showers, hand-me-downs, and gifts after the baby is born, having enough clothing is the typically the last thing new parents need to stress about purchasing. And if they do find themselves in need of more tiny t-shirts, there's no harm in asking relatives and friends for clothes they no longer need.

"Kids are going through a lot of things in their first few years that they really don't even need and they're so small, they don't even have any concept of what's going on around them," Horack says.

So go ahead and use the onesies your sister gave you - and save your own baby budget for more important items.