I have a 3-month old baby and she is starting to have control of her neck and head. She's also gaining weight that sometimes it strains my arms whenever I carry her for a long time in a lying position. My husband thought of getting her a baby carrier so it would be easy for us to move around most especially when doing errands. Is it safe for this age to be placed on a vertical/standing position? What is the ideal age for infants to use a baby carrier?