Best Answer: smile at 6 weeks, laugh 2-3 months, sit up 6-9 months, roll over one way 3-4 months. Just averages all babies are different. Sign up for this. It will give you monthly newletters about development and milestones and they will also send you coupons, samples and a free baby's first year calandar with stickers: http://www.verybestbaby.com/Public/Default.aspx.