To be honest, there other people on the forum who walk with children a lot more than i do (Enter Mr B and others) but i can comment on how to keep the motivation up on LDPs.
First; Try not to focus on the end of the LDP, to much. It is nice to imagine how you will finnish and how much you have covered but try and not think about it all the time.
2. Make your goals, small and meduim goals. i.e; the walk you are about to do that day, break it into two. The morning section, then break......................... the afternoon section.
3. Read up on the area and the days walks, so that you can pass on as much information as you can, this helps make the walk a lot more interesting to yourself and others.
4. With children, sometimes it is good to make up stories about the area and the walk. (i also do this with adults).
5. Find places that will interest yourself and the people you walk with and try to vist them.
6. Remember it is NOT a race.... If you find that you need to stop, then stop. After all you are there to enjoy it, if you find yourself or others just walking and looking at the ground, then you are losing the reason of why you are all there.
7. You would be amazed, at how good a warm shower, a warm meal and a good conversation can lift the soul.
I like to finnish on lucky 7, so P.s- What ever you do dont carry to much weight and remember that just by starting a LDP, you have gained so much for yourself and others with you, i really does'nt matter if you finnish it in one go or more. (i know there are some who would disagree but i think the achivement is already there)
Hope this helps, i am sure there will be others that can add to this advice, Mr B, W/G ect