I don't know what I would have done without Sweet Pea's carrier through her colic phase. Wearing her in that carrier was the only thing that would calm her down between the hours of 7pm-10pm nightly. And it worked nearly every time. (I just couldn't sit down.)
That's why I was concerned when I read this about the hazards of baby carriers and baby seats on baby's motor development and cognition. I decided to search for evidence-based articles and share my findings here.
Most of the research done on these devices is in regards to baby walkers. Pediatricians and Family Doctors advise against using a baby walker for good reason. (I was surprised to see them still sold in baby stores.) The main reason to avoid baby walkers is that they can lead to injury, such as skull fractures from tips and falls down the stairs. From data I read, injuries resulting in visits to ER from baby walkers are not uncommon.
Additionally, research has shown that baby walkers actually delay walking and crawling in infants. Also, I found evidence that use of baby walkers was correlated with lower scores on mental development (in infants 6-15 months). The authors explained that walkers by design limit visualization of the infant's moving legs. When infants used the walkers, they were deprived of visual feedback important for neurodevelopment.
The Bumbo seat has received some bad publicity lately, due to reports of severe injuries from falls in the seat. It should never be used on an elevated surface.
I actually like the Bumbo seat, as long as it is used appropriately. Both Peanut and Sweet Pea enjoyed/enjoy being able to sit up to see everything in this chair. And, since babies should be put to sleep on their backs, they do end up spending a lot of time on the back of their heads. We've seen an increase in the cases of "positional plagiocephaly" (or flat back of the head) in babies since the "back to sleep" campaign. (Still, we must put babies to sleep on their backs.) The Bumbo helps babies spend less time on the back of their head.
Per my literature search, I could not find any studies relating baby chairs to motor development or neck/back strain. As far as I could find, information regarding potential harm of baby's neck and back is theoretical. Although, the theory does make sense to me. Babies develop their strength from the head down, which is why the Bumbo works to keep an infant upright. Babies neck is strong enough to be held upright before her core is ready to support the seated position. The Bumbo supports the back/core while the neck does the work to keep baby upright, creating the potential to strain the neck if left in the seat too long.
I used the Bumbo with both Peanut and Sweet Pea once they each were about 4 months old and once they had very good neck control. I would not recommend using it before 3 months of age. I am within an arm's reach of Sweet Pea while she enjoys the chair and I only leave her in the chair for about 5 minutes at a time (she's 4 months old now). Once she shows any signs of fatigue, I take her right out.
Please, never use a Bumbo on an elevated surface. These chairs may topple.
Exersaucers were meant as an alternative to baby walkers, because they are essentially a stationary walker, which also includes activities around the circle. I did not find any studies regarding harm of motor development that have been done yet, but I think we will find many of the risks of the baby walker will apply. (Again, infant is not able to see her feet when she pushes off the ground to rotate the exersaucer.) These devices can still topple, but at least they are not as likely to go down the stairs. We never had one of these - I figured Peanut and Sweet Pea wouldn't stay in them long enough for me to go to the bathroom anyway. I think moderation is the key here (as well as safety and monitoring baby while using).
I honestly don't know what I would do without mine. When Sweet Pea is crying if put down, and I need to get Peanut through the bedtime routine while Daddy MD is at work, Sweet Pea goes in the carrier. And, colic would have been impossible to survive without the carrier for me.
The reported risks with baby carriers include the risk of asphyxia especially from the sling design, where babies neck can become to flexed, inhibiting breathing. Here is a good diagram for positioning.
Additionally, we want to make sure that an infant's head and neck is adequately supported. For my girls, I didn't use one the first month of life. I felt like I needed to hold their necks with one hand if they used it early on.
I also was concerned that Sweet Pea would get stiff riding in the carrier, just as you and I would become stiff if forced into one position for a period of time. Even in the womb, the baby can kick out her arms and legs. In some baby carriers, I feel that the limbs can be too restricted.
My bottom line on carriers: Many babies love them. Many moms love them. We can tend to other duties while our baby is content and we feel closeness with our baby. Use them in moderation and allow plenty of free movement and stretching time for baby.
Babies don't need expensive activity chairs. Babies need a safe place on the floor to self explore and plenty of supervised tummy time. We should create a safe environment where babies can reach milestones naturally.