While starting school is an exciting time for your child, the transition can be difficult for the younger sibling left at home. Suddenly their beloved companion and playmate has disappeared and they find it hard to understand why they can't go along too. 
These tips will help your youngest child adjust to the new arrangements.
Make sense of the situation: As well as not understanding why they can't go to school, your child might be struggling to manage their feelings. Explain that they're feeling sad because they miss their older sibling and that you feel the same way, but that you'll both see them later. You can explain that they'll be able to go to school too when they're older and distract them with tasks to help them train for school, such as learning the alphabet.
The plus side: Show your child the benefits of it just being the two of you in the house.Set aside time to do fun activities together such as make-believe games or colouring. Let them see the benefits of spending quality time with you.
Distract them: Bring your child to new places outside the house. Go for walks, visit parks, join a playgroup or introduce them to the library. Being away from a place they associate with the missing sibling will help take their mind off the situation.
Substitutes: Arrange play dates for your child. They may feel like their older sibling is the only person they can play with and introducing new children into their lives will show them that there are other people who can fill the role.
Create a routine: Bring your youngest on the school run in the morning and let them come along when you pick your child up from school. This will make them feel secure in the knowledge their older brother and sister will always come home. Try and schedule some time after school for the two of them to play together for a little while.