The longer I've been a Mom, the more I realize that you can generally monitor the age of a baby simply by observing the diaper bag his mother uses. Here are my very unscientific findings:
Stage I: Enormabag
This stage is reserved for the very small baby. Especially first time Moms tend to want on hand several outfits, about a jumbo pack of diapers, a wide array of bottles, burp cloths, and just about every cream and lotion ever labeled for infant use. This stage lasts for about 5-6 months for first-time Moms and 2-3 months for professionals.
Stage II: Multi-pocket Big Bag
As a newborn progresses, the need for all the gadgets starts to diminish. At this age, Mom is fascinated with many pockets to quickly organize the still somewhat abundant baby storage receptacle she carries. If the Mom has other children, this is compounded as the family is feeling more up to going places with a baby that is a little farther into the infant years. When you have other children, you need pockets for little boy cars, snacks for the toddlers who are jealous seeing baby eat, potty training outfits and/or diaper products, and sometimes also miscellaneous stuff for your husband. This stage lasts until the baby is 9 months for new Moms and until 5 months for returners.
Stage III: Big Bag with Purse
This is the stage where your baby gets so heavy, you're getting tired of lugging things around. Moms shove only a moderate amount of baby gear into the bag (no pockets necessary...it's always a mess anyway). You strategically leave enough room on top of the baby things to stuff your purse in on top, thus creating one less thing to keep track of. Amazingly, you can get everything you need for an eight hour period in one large bag! This is where the ages begin to vary according to the mother's muscle tone and ability to remember where things are. Returning Moms are stronger, but have shorter memories than newbies!
Stage IV: Large Purse
This is the stage where I currently am with my daughter. Moms reach this stage whenever their pride/tolerance level tires of looking like a pack mule all the time. You gradually enter this stage, dipping in an outing at a time, then progresses to full time. The trick to this stage is to have a purse large enough to hold everything you need normally, as well as 2 diapers, a ziploc bag of wipes and a small snack.
Stage V: Stray Diaper
By the time a Mom gets to this stage, her baby only needs to be changed a few times a day. Mom also is laid back enough to assume there will be wipes or something you can use as wipes around most anywhere you go. Baby is usually on full table food at this stage...you don't usually see stray baby food jars laying around. Stray diaper quite often stays in the glove box of my car, sometimes in my purse, or I simply let baby hold it until we get to the church nursery or wherever we are going. Here's a note...Moms stay in this stage until potty training begins, at which time they revert back to Stage II or III temporarily and retrace the journey through to stray diaper. At the end of potty training, it's more of a stray underwear/pullup thing, but after that, you're home free...until you have another baby, that is.