i have 4 kids - 15 months apart, 26 months apart, and 14 months apart (so when i was late in preg with 4th child, 1st child was 4 yrs old. i never stopped pickin them up if they needed a cuddle, put in a carseat, or put to bed etc - only thing i restricted myself on was how long i held them for ie - if they were capable of walkin down the street holdin my hand, then i wouldnt go out of my way to carry them while walkin (if that makes sense!)... Listen to ur body, it'll tell u wot u can and cant do, and for how long :-)
i asked my OB last week- as i went into his office with my 18 month old on my hip... he said no restrictions.