He could feel neglected now that there’s a younger sibling. Try to give him a role in caring for your younger child, so he feels involved and not neglected? Also see if your oldest child can play with him? He may not like playing with other kids yet, but going for play dates or play group may help (note: sanitise his hands frequently, because you don’t want him falling sick). Also, if you can have someone help with your youngest child sometimes, set aside some time every day with your son, and make it quality time, so he knows you love him.
So how do you help your toddler learn social skills? 1. Empathize, empathize, empathize. 2. Stay close during playgroups. 3. Don't force toddlers to share. 4. Let the child decide how long his turn lasts. 5. Help your child wait. 6. Intervene with compulsive grabbing. 7. Teach assertiveness.
Arrange playdates or join a playgroup
Bring him out more often