I LOVE LEXAPRO!!! I suffered from horrible anxiety and insomnia for years before Lexapro. I tried many other medications before Lexapro came on the market - I've been taking it since about six weeks after it came onto the market in 2002. Lexapro has by far the fewest side effects - at least for me.
Yes, if you stop taking it suddenly, you will have withdrawals. (I once went on vacation and forget to pack it... NOT good.) However, as any good doctor will tell you, you have to wean off an SSRI. I have had to quit taking it three different times to do IVF (my RE is very conservative...) and never had a problem with withdrawals. My doctor had me wean off it over a three to four week period. After each IVF I went right back on it either after the first trimester or after a negative pregnancy test.
If you are certain that your insomnia is causing your anxiety, you might want to try something like diazepam or lorazepam that will relax you enough to sleep, but won't completely knock you out so that you can wake up to tend to your son as needed. However, if the anxiety is causing the insomnia, I think you'll really like Lexapro.
It doesn't matter what time of day you take it, this is a medication that needs to build up in your system to work.
Again, don't worry about withdrawals. If you decide you want to stop taking it, you just need to wean slowly and you won't have a problem.
Good luck!