For partners, you can select which partner is current and which is/are ex-partners. This is shown by a thicker line on the tree.
For children it can be slightly more tricky. If you don't know their dates of birth, I would advise just putting numbers in the DOB years' section, eg the oldest child is 1, the second child is 2, etc. This will rearrange the children in order of birth.
If a person has had more than two partners and you want to put them (the partners) in order, (because a thicker line to the current partner will not distinguish between the exes) you can use the number trick in the wedding & divorce/relationship start & separation dates to do this. Note that this may not re-order them on the tree.
Your question seems to ask how to re-order people without going to the trouble of entering lots of information. However, just using numbers in the date bars as described above is a quick and easy way to order people, and even if a feature like the one you describe is implemented, it is hard to envision one which is entails less work than the numbers do.
Hope this helps!