A lot of parents of toddlers and preschoolers will have had the very frustrating experience of their child insisting on everything being done in exactly the same way again and again. Vegetables must be on the top of the plate, shoes must be put on before coat, teeth brushed after bath, bedtime story must be read in exactly the same way - no changing the voices - the same bowl for breakfast and one cup for juice, a different one for milk, and woe betide anyone who tries to change this.
Well, you'll be reassured to know it IS just a phase - it's a very common phase - and there may be some explanation for it.
As children grow older, they become better at behaviours called "executive functions". This set of behaviours particularly helps children to be more flexible and less focussed on the here and now. So one classic test of executive function asks children to sort cards that have different coloured shapes first by the colour that is on them - and then to switch to sorting by the shape that is on them. Younger children tend to stick to the same sorting method; they are very driven by what they are already doing. Children in this stage find it really difficult to play games like Simon Says - they can't switch from "do what I say" to "don't do what I say", and they find resisting tempting behaviours really hard - put a sweet in front of them and ask them to wait for permission to eat it, and it will be gone before you blink. They respond to what they see, and find it hard to control their own behaviour to respond in a different way.
It's been found that these types of executive functioning are quite closely related to the ritualised behaviours that toddlers and preschool children are so good at. It seems as if as children get older and have more control over their own behaviour, ritualised behaviours decrease - a great relief to parents. Recent research suggests that this is broadly true, but with a slight difference as children get older. Younger children showed some relationship between ritualised behaviours and executive function but in older children this was even stronger - although it's not possible to tell from this study, this could be because if older children (especially those of young to mid-primary school age) have these ritualised behaviours, it's definitely because of somewhat poorer executive functioning, but in younger children all of the children have these behaviours to some extent.
We do know that executive functions improve with practice, though. So it's not necessarily a case of just waiting it out until your child, and their brain, are mature enough to live without the ritualised behaviours. Although no-one's done any studies linking this directly to ritualised behaviours, another study trained 4 to 5 year old children using a stop-go game in which they had to sometimes respond and sometimes hold themselves back. Training on different games - such as the card sorting game - helped children to stop themselves from responding inappropriately on the stop-go game.
So although waiting it out should mean you can put away that essential Iggle Piggle plate eventually, helping children to think more flexibly by practicing games and behaviours where they have to exercise self-control will at least give them the skills they seem to need to grow out of the rituals.