Liam is 4 months

Today Liam had his 4 month wellness check-up.  The stats are:

Height: 25.5 inches (he grew 2 inches in 2 months)

Weight: 15 lbs. 13 oz. (he gained about 3.5 lbs in 2 months)

The doc jokingly said "I don't need to ask how your milk production is going, huh?".  Ha ha.  She said he used to be at the 60th percentile but Liam is now at the 80th percentile.  However I am confused.  I looked back at the stats for Gavin at 4 months and Gavin was 25 inches and 15lbs 12oz--pretty much the same yet we were told that he was at the 50th percentile.  I know the percentiles are not differentiated by much but one ounce cannot equal that much of a difference.  

Anyhow, we are happy that Liam is healthy and chunky. 

Side note:  I find it funny that we have these sayings like "smooth like a baby's butt" yet Liam's butt is all cellulite (and Gavin's was too) and also "sleeping like a baby"....whose baby?  Mine sleep in 3 hour blocks!??!?  I want to sleep like a teenager!!!