How do I tell my morbidly obese dad I don't think he can babysit?

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So my dad is really big! Like 550 or so. He can walk but not too good. Lately I've been looking for a babysitter and he keeps mentioning himself! My baby is 10 months and crawls so fast everywhere! He wouldn't be able to bend down, pick her up, or anything! And i also don't like ANY male changing my babys diaper but her dad. My dad is really sensitive about his weight and the most he can do with her is have her sit on his belly and play. How do i tell him in a nice way? If she fussed, he wouldn't be able to set her down then make her bottle, then put her to bed etc. He told me "well I did it with you" but he was in the navy and also had the help of my momma and her 4 other kids before me.