18 month old hurt leg

My 18 month old and my 4.5 year old we’re playing together in the living room while I was cooking dinner. I heard my 18 month old start crying pretty hard and rushed to see what happened. My 4.5 year old says “I don’t know what happened” and my 18 month old is having a hard time standing up, he keeps falling over so I pick him up and console him. But when I put him back down, he once again cannot stand. After a few minutes, he’s able to walk, but he’s walking really funny. Like he won’t put weight on the leg that’s hurt. He’s not crying anymore, but he won’t run and is walking super slow and limping. How concerned should I be here? He doesn’t seem to be in pain. He’s laughing and playing like usual, just not running or anything. I’m thinking maybe he’s just sore, but I’m also thinking maybe we should go to urgent care and get x-rays. Any thoughts?