DS1 is 7. Always been quite tall - 75th centile or thereabouts. Had him weighed yesterday and he's 21.5 kgs - about 3st3. He's 125cm tall. I blew the dust off his red book and he weighed 20kg at 5!
Is it usual for kids to put on this little weight in 2 years? He may even have lost - I'm sure I remember him being 22kg at some stage. He has had a height growth spurt recently (and a show size spurt).
I am sure if he eats well and is well in himself then he is absolutely fine. My DS1 stayed the same weight (but grew in height) for 15 months but he was just stretching out as he was a roundish pre-schooler and had changed shape a bit. Maybe he has had a growth spurt upwards and will fill out a bit now?
I remember my brothers being particulary skinny at around the age of 7 and they could eat for Britain! They are both 'normal' size now Sadly I do not share their body type