Update to my last post?

I would like to thank you all for your advice on my last post. I took my puppy to the vets earlier today. She checked him over after i had explained to her what was going on. She said he is an over confident puppy that is trying to get ahead of me in the "pack". She also told me this behaviour is common in dogs aged 12-8 months, she has never seen it in a puppy of 5 months and its a little worrying. She has recommended i get him castrated as soon as possible before he hits "puberty" as things may get out of control if he continues with this behaviour. She recommended that i also buy a harness and i attach a lead to him so i can remove him without having to touch him. She assured me that with the kids it was just playing. I also mentioned i was due to be getting another puppy in just over a weeks time did she think it was a good idea. She said she thinks it would be a good idea as it would give him someone to play with also it may calm his confidence down slightly as he will tire himself out and give him someone to show what is what. I did mention as well because some people have told me it is my fault for not training him properly, she assured me that his basic training must be fine because he responds to commands my 4 year old gives him but he doesn't see her as a threat because she is not top dog. I just hope castration works, he is booked in next week, by which time he will be 5 and a half months old. I will keep you posted