I put my 1st son in a Babytrend jogger at 6 weeks, but I did use one of those neck supports that you use in a car seat. I've got an InStep 10K model on the way (double stroller this time), and the literature suggests waiting to 3 mos... but both of my sons are/were pretty big kids, so if Robby (baby #2) seems comfortable in it while propped up, I'll put him in at 6 weeks as well.
Susan
