I'm 14 and have started lifting weights, i do 3 sets of 10 every time and when i can do that easily i add some weight, is this ok as i don't want to affect my growth.

10lb sound heavy for a 4 year old although how is he lifting it, eg; curls.

Lifting weights will NOT stunt your growth, no matter what your age!!! Why do people keep perpetuating this falacy?

You can injure yourself if you try to lift maximal weights, but doing sets of 10+ reps is unlikely to injure anyone, if you use reasonalble form and common sense!

Lifting weights CAN stunt your growth, if you do it wrong. I would suggest light exercises of 10-12 reps, don't go under 10. And learn all the movements prior to attempting them. As long as you take precaution you'll be fine.

Ya i woudln't do anything more than his own body weight. I would say that his motor skills are still develloping so he his own body is enough to help him get stronger and fitter. For running i'd have him doing sprints to get him faster. He doesn't raelly need to do endurance that bad if he's running around. Plus he would probably hate it and not want to play w/e sport you want him to. Don't push him too hard.

i tink it would be more effective if he did a sport, there are always kids who get muscly just from the sport they do, get him to do basketball, rugby, american football. or waterpolo thats very good.(swim incl)
ur better off getting muscle like that than with weights at such a tiny age.
my friend(he is 15) got very big muscles just from waterpolo. so i would tink sports is better right now.

Right now, I'm picturing in my mind a 4 year old doing deadlifts and back squats

I would highly recommend doing some mild research on a condition called Osgood-Schlatters disease. I got it and it's not fun at all. Basically what happens is that if you really push yourself before your bones are fully developed and grown and hardened, basically your quad muscles can slightly rip the ligament off of your shin bone over and over, and EXTREMELY SORE knotty scar tissue will grow around this area. I am 30 and I still have a knot that is slightly sore, but it takes a bigger hit than it used to in order to cause pain. When I first got it, the least little thing that hit it had me on the ground in the fetal position holding my knee in pain. That's not exactly high-quality childhood memories right there. The memories of starting playing team football at age 7 and going to nationals in track at age 12 were awesome, but the knee pain was hell.

That being said, I see no problem in doing extremely lightweight things just to get him excited about exercise and learning properly. I would keep it on the same level or lower than what he's doing for play though. Don't go beyond that and you should be fine. Basically I would recommend only doing things to get his self-esteem up and let him feel that he's getting to hang out with his dad and be like him, even if that means only going through the motions. I would definitely NOT recommend actually trying to devise a way that he's actually packing on muscle due to the above paragraph, and there are worse things that can happen than what I mentioned.

Remember that running and jumping will can put up to 6X your bodyweight of stress on your joints. Liftins 5 or 10 lbs will hardly make a difference by comparison.

Problems occur when a child does too much of a repetative movement.

Also remember that this is a kid. There will be plenty of time to do some super cool training later on. Right now keep things fun.

Holy **** ? u give ur son who is 4 years old to lift weights man are you out of ur mine please with until he gets at least 15 years old and leave him to dicied if he wants to lift weights or not. lifting weights can harm major injures to kids at age new born- 11 years old... . Man it doesnt matter how much u give him to lift 2 Ib, 10 Ib or 100 Ib its still very harmful for a kid at age of 4. Lol if u want him excercise or something let him play with some friends and run around... and something else if u want him to be in better shape when he grows up then sign him in a swiming courses it will be really fun and good for his health, then lifting weights... and btw if 10 Ib are little for u i dont this that for kid that weights 27 Ib is little ...