Have you been carrying him on your front or back twag? I used to have a Manduca - we loved ours. We have another kind of buckle carrier now. It's completely safe to continue to carry them. I've been back carrying my hefty 15 month old with no problems. I just sit the waist band above my tummy and carry her on my back. I carry her a fair bit still. I just stop when I get a bit achey. X