2 and 3 year olds are just learning about sitting in a group setting and staying in their spot. If they have a preschool mat that is just the right size for their feet, it can help them stay in the right spot.
We found these little mats at Target. They were about $3 each and are just the perfect size for preschoolers. When it’s time to start Large Group, we play the clean up song. Preschoolers help to clean up all the toys, and then they go get a preschool mat. They put their mat on the floor and during Large Group time we get them to sing songs & stay on their mat. During story time, they sit on their mat. They often need to be reminded to “stay on their mat” but at least it gives them a defined space where they need to stay. Preschoolers love to help so when the Large Group time is over, they pick up their preschool mat and put it back in the pile with the other preschool mats.
Placemats can be a good choice if you need a small space for a preschooler to stand. Pillows are another way to create a spot for preschoolers to sit. Carpet squares can be another alternative. You can usually get them from a carpet store when they have old samples they need to get rid of.