Exersaucers and jumpers are not meant to be used until your baby is naturally pulling himself into standing. Some parents think that they can use these items as soon as baby has some trunk support and can hold his head up, but this could do your baby a disservice.
Her tiny muscles and ligaments of her feet, ankles, knees and hips are not prepared to bear her weight until she is naturally pulling herself to standing. Weight bearing too early could result in knock-kneed children or bow-legged children because of the structural instability at such an early age.
Exersaucers and jumpers are nice for teaching balance and core strength when introduced at the right time.
* Always make sure your baby is able to weight bear on flat feet, not her tippy toes. If she can only reach the floor with her tippy toes and the device is on the lowest setting, but a pillow or large book underneath her feet so she can get her heels down to the floor. She should not weight bear for long periods of time on her toes.
***Walkers should not be used at all! They are illegal in Canada and should be illegal in the US as well. They are a hazard as children can reach dangerous counter tops, fall down stairs, and severely injure themselves.
References:
American Academy of Pediatrics Committee on Injury and Poison Prevention. (2001). Injuries associated with infant walkers. Pediatrics. Vol 108. http://pediatrics.aappublications.org/content/108/3/790
American Academy of Pediatrics. (2018). https://www.aap.org/en-us/advocacy-and-policy/aap-health-initiatives/HALF-Implementation-Guide/Age-Specific-Content/Pages/Infant-Timeline.aspx
Healthychildren.org (2018). https://www.healthychildren.org/English/safety-prevention/at-home/Pages/Baby-Walkers-A-Dangerous-Choice.aspx
Kelly, P. (2016) First year Baby Care. Meadowbrook Press
Mayo Clinic. (2018). https://www.mayoclinic.org/healthy-lifestyle/infant-and-toddler-health/expert-answers/baby-walkers/faq-20058263