I think 11-1 or 12-2 is best. If not then 3-5. I hate it when parties don't cover a mealtime. Or, go with squirrels suggestion and don't try to feed them too much.
2-4 I have to give them lunch at home, try to get DD to have a sleep, wake her early then go to party where they eat sufficient food for them to not want tea at 5ish but are hungry at bedtime.
11-1 - breakfast, lazy morning, go to party, come home where DD will sleep and DS can play. Rest of the day as normal. After DS's party it meant he had all afternoon to open his presents and play with them.