I don't know about weight but the the strollers "specs" says one child up to 5 for the single and two up to 5 for the double. At AK, MK and Epcot I think could rent a double for him to be comfortable but you may have a hard time pushing him around. I don't think the MGM strollers would accomodate him at all. I would try and start walking prior to the trip and do as much walking in the parks as he can. My girls are 5 & 7 and do fine at MK, MGM and AK, the place we are most likely to need a stroller is at Epcot - it has much more walking and we also tend to stay there later. Go to wdwig.com and check the link for stroller FAQ's they have a picture of the singles and doubles at each park. I found our trip so much more enjoyable this time without the stroller to worry about! YMMV
Have a great trip
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