Baby falls down and walk zigzag way.

Dear doctor , My baby is 1.8 years old and weight is 12.3kg... on 26 Jan when he was playing running he falls down suddenly on his knees and from that time he was not able to walk properly..on that night he was not able to put his legs down, next day he was not able to bend down the leg to collect the toys but in next days he Abe to walk and run... but today is 9th day and still he walk and run in zigzag way... he has No fever. So swelling also we press his right leg put he has no pain...then why he still walking in that way we are not understanding..any major problems??? Any weak bones issues? Or something else?? I m very much tensed now ..on that day he was facing loose motions problems but doc suggested to give econorm sachet..now his stomach is fine..but he still not walking properly but baby is active...now what to do m not understand..pls help with resolution 🙏