If you go to WDW in September, it is hotter than DL in June or July. Heat is relative. When we go to DLR and people are complaining about how horribly hot it is, it always feels fine to us. We have been to DLR in June or July for the last 7 years. The first year we went in July, I was really worried about how crowded it would be and I was pleasantly surprised. DLR isn't awful in the summer by a WDW vet's standards. It is what I call moderate. The most crowded days we have had at DLR have been on the Monday and Tuesdays in early June when it is some of the very last days the passholders have before being blocked for the summer. Those two days are crazy busy. Those should be before your trip. Avoid those couple of days, and you should be fine. By the 3rd week of June, you will probably be in shorts and short sleeves day and night. In early June, it is cool in the mornings and evenings and warm in the afternoon. More than once, I have bought a sweatshirt/jacket in the evening for DD or myself at DL/CA (and yes- I know I could come prepared and carry one in the park with me and drag it around all day, but where is the fun in that!). In July, I have never been cold. Also, if you are rope drop people you will love it at DLR. The parks usually open at 8:00 a.m., and because a lot of the people are local, from 8:00 -10:00 a.m., it is typically very low crowds. It is way less than you find at WDW at rope drop at moderate times. We can get a ton done in those first 2 hours.