We've not missed in more than 20 years. I presume that you're talking about going on Saturday for the cross country. We prefer to go on an earlier day - usually Thursday - because the shops (a highlight for many) are rammed on Saturday and we don't want to miss the horses anyway.
Yes they have a dog crèche but I wouldn't take one..
I wouldn't expect a 4yo to walk the whole course. It's massive and really hilly.. I'd head for the main water complexes and base yourself there for quite a few horses. They have a big screen at Trout Hatchery which is helpful.
Take a picnic blanket to sit on and/or small stools/chairs as this will make it much more pleasurable.
Remember to get there really early. We aim to be in by at least 9am otherwise you spend lots of time queuing and are miles away.
We do walk most of the course but do it in reverse. Find it better than going with the herd.
Remember it is massively busy - one of the biggest sporting events in Britain of the year on the Saturday. Even Thursday and Friday are busy with shoppers and dressage fans. There are plenty of places to buy food from (we like the stalls near the water splash) but I would still take my own food for picnicking on way round.
Remember though that the food part of the shops is second to none - there is no type of food they don't sell there although sadly the scotch egg specialist isn't going to be there this year.
If planning on going Sunday you may need to consider buying grandstand tickets (if not already sold out) to watch the show jumping. We watch the working hunters in the other ring instead.
I wouldn't recommend buying Members badges if only going one day. It is better to have has a base for the week whereas you'll be out in the country on Saturday.
The shops are fantastic and don't forget they open early and close late. There are loads of stalls in the various marquees as well as main big ones.
They do specialist talks down at the square near the posh marquee (can't remember it's name) which is also the area for the best equestrian stalls and feed merchants.
It is an overwhelming experience !!