The proper perspective is “so what?” So what if he squirms when you are trying to change him? So what if changing him takes three minutes instead of two? So what if he stands up in the tub? Just steady him with one hand and wash him with the other. Or, wash him in the kitchen or laundry room sink so that you are standing up and can exercise more physical control of him while he's standing.
So what if he slaps you in the face? At this age, this is not purposeful aggression. When it first occurred, it was random. Your reaction — startled? angry? — interested him, and he wants to see it again. The solution is (a) to do your best to not put your face within striking range, (b) to intercept as many slaps as you can, and (c) react nonchalantly when an attempt to intercept isn't successful.
The attempt on your part to entertain and make things fun may be part of the problem. Without intention, your “entertainments” may be exciting him and stimulating his activity level.
You may believe, as do many of today's moms, that you should be constantly talking to your child in order to promote “bonding” as well as proper language development. There's a grain of truth in that, but it's not much more than a grain. When mothers didn't have lots of time to devote to their children, children still learned how to talk and talk well.
If all you did was sing one of your favorite songs while you're changing your son, for example, that's language stimulation enough. In other words, you don't have to be talking directly at your son for him to develop good language skills. And when you do talk to him, your tone does not have to be upbeat and “entertaining.” It can be very matter-of-fact, in fact. You do not have to make everything seem fun.
Fifty-plus years ago, before robotic vacuum cleaners, programmable washing machines, and microwave ovens, mothers didn't have time to pay lots of attention to their kids. They paid enough. And when they did pay attention, they didn't act like cruise ship recreation directors. And their kids seemed to have turned out reasonably well.
Family psychologist John Rosemond answers parents’ questions on his web site at www.rosemond.com.