Check up on
Definition 1 of 2
Pro Tip 1/3Caring Context
Used when showing concern for someone’s well-being or status. 
I'll check up on Sarah later to make sure she got home safely.
Pro Tip 2/3Not Intrusive
It implies a gentle inquiry, not an aggressive investigation. 
Could you check up on the kids without waking them?
Pro Tip 3/3Follow-up Action
Often suggests a subsequent action or additional help might be offered. 
After checking up on your brother, offer him help with his homework.